Stephen Collie Enterprises New Zealand

This post was written by Jeremy Davis, JavaScript Developer for Toptal.

CSS was designed for documents, what the “old web” was expected to contain. The emergence of pre-processors like Sass or Less shows that the community needs more than what CSS offers. With web apps getting more and more complex over time, CSS’ limitations have become increasingly visible and difficult to mitigate. Styled components leverages the power of a complete programming language—JavaScript—and its scoping capabilities to help structure the code into components. This helps to avoid the common pitfalls of writing and maintaining CSS for large projects. A developer can describe a component’s style with no risk of side effects.

What’s the Problem?

One advantage of using CSS is that the style is completely decoupled from the code. This means that developers and designers can work in parallel without interfering with each other.

On the other hand, styled-components makes it easier to fall in the trap of strongly coupling style and logic. Max Stoiber explains how to avoid this. While the idea of separating logic and presentation is definitely not new, one might be tempted to take shortcuts when developing React components. For example, it’s easy to create a component for a validation button that handles the click action as well as the button’s style. It takes a bit more effort to split it in two components.

The Container/Presentational Architecture

This is a pretty simple principle. Components either define how things look, or they manage data and logic. A very important aspect of presentation components is that they should never have any dependencies. They receive props and render DOM (or children) accordingly. Containers, on the other hand, know about the data architecture (state, redux, flux, etc.) but should never be responsible for display. Dan Abramov’s article is a very good and detailed explanation of this architecture.

Remembering SMACSS

Although the Scalable and Modular Architecture for CSS is a style guide for organizing CSS, the basic concept is one that is followed, for the most part automatically, by styled-components. The idea is to separate CSS into five categories:

  • Base contains all the general rules.
  • Layout’s purpose it to define the structural properties as well as various sections of content (header, footer, sidebar, content, for instance).
  • Module contains subcategories for the various logical blocks of the UI.
  • State defines modifier classes to indicate elements’ states, e.g. field in error, disabled button.
  • Theme contains color, font, and other cosmetic aspects that may be modifiable or dependent on user preference.

Keeping this separation while using styled-components is easy. Projects usually include some kind of CSS normalization or reset. This typically falls in the Base category. You may also define general font sizing, line sizing, etc. This can be done through normal CSS (or Sass/Less), or through the injectGlobal function provided by styled-components.

For Layout rules, if you use a UI framework, then it will probably define container classes, or a grid system. You can easily use those classes in conjunction with your own rules in the layout components you write.

Module is automatically followed by the architecture of styled-components, since the styles are attached to components directly, rather than described in external files. Basically, each styled component that you write will be its own module. You can write your styling code without worrying about side effects.

State will be rules you define within your components as variable rules. You simply define a function to interpolate values of your CSS attributes. If using a UI framework, you might have useful classes to add to your components as well. You will probably also have CSS pseudo-selector rules (hover, focus, etc.)

The Theme can simply be interpolated within your components. It is a good idea to define your theme as a set of variables to be used throughout your application. You can even derive colors programmatically (using a library, or manually), for instance to handle contrasts and highlights. Remember that you have the full power of a programming language at your disposal!

Bring Them Together for a Solution

It is important to keep them together, for an easier navigation experience; We don’t want to organize them by type (presentation vs. logic) but rather by functionality.

Thus, we will have a folder for all the generic components (buttons and such). The others should be organized depending on the project and its functionalities. For instance, if we have user management features, we should group all the components specific to that feature.

To apply styled-components’ container/presentation architecture to a SMACSS approach, we need an extra type of component: structural. We end up with three kinds of components; styled, structural, and container. Since styled-components decorates a tag (or component), we need this third type of component to structure the DOM. In some cases, it might be possible to allow a container component to handle the structure of sub-components, but when the DOM structure becomes complex and is required for visual purposes, it’s best to separate them. A good example is a table, where the DOM typically gets quite verbose.

Example Project

Let’s build a small app that displays recipes to illustrate these principles. We can start building a Recipes component. The parent component will be a controller. It will handle the state—in this case, the list of recipes. It will also call an API function to fetch the data.

class Recipes extends Component{
  constructor (props) {
    this.state = {
      recipes: []

  componentDidMount () {

  loadData () {
    getRecipes().then(recipes => {

  render() {
    let {recipes} = this.state

    return (
      <RecipesContainer recipes={recipes} />

It will render the list of recipes, but it does not (and should not) need to know how. So we render another component that gets the list of recipes and outputs DOM:

class RecipesContainer extends Component{
  render() {
    let {recipes} = this.props

    return (
        { => (<Recipe key={} {...recipe}/>))}

Here, actually, we want to make a tile grid. It may be a good idea to make the actual tile layout a generic component. So if we extract that, we get a new component that looks like this:

class TilesContainer extends Component {
  render () {
    let {children} = this.props

    return (
, (child, i) => (
            <Tile key={i}>


export const Tiles = styled.div`
  padding: 20px 10px;
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;

export const Tile = styled.div`
  flex: 1 1 auto;
  display: flex;

  & > div {
    flex: 1 0 auto;

Notice that this component is purely presentational. It defines its style and wraps whatever children it receives inside another styled DOM element that defines what tiles look like. It’s a good example of what your generic presentational components will look like architecturally.

Then, we need to define what a recipe looks like. We need a container component to describe the relatively complex DOM as well as define the style when necessary. We end up with this:

class RecipeContainer extends Component {
  onChangeServings (e) {
    let {changeServings} = this.props

  render () {
    let {title, ingredients, instructions, time, servings} = this.props

    return (
          <input type="number" min="1" max="1000" value={servings} onChange={this.onChangeServings.bind(this)}/>
          {, i) => (
            <Ingredient key={i} servings={servings}>
              <span className="name">{}</span>
              <span className="quantity">{ingredient.quantity * servings} {ingredient.unit}</span>
          {, i) => (<p key={i}>{instruction}</p>))}

Notice here that the container does some DOM generation, but it’s the only logic it contains. Remember that you can define nested styles, so you don’t need to make a styled element for each tag that requires styling. It’s what we do here for the name and quantity of the ingredient item. Of course, we could split it further and create a new component for an ingredient. That is up to you—depending on the project complexity—to determine the granularity. In this case, it is just a styled component defined along with the rest in the RecipeStyles file:

export const Recipe = styled.div`
  background-color: ${theme('colors.background-highlight')};

export const Title = styled.div`
  font-weight: bold;

export const Ingredients = styled.ul`
  margin: 5px 0;

export const Ingredient =`
  & .name {

  & .quantity {

For the purpose of this exercise, I have used the ThemeProvider. It injects the theme in the props of styled components. You can simply use it as color: ${props => props.theme.core_color}, I am just using a small wrapper to protect from missing attributes in the theme:

const theme = (key) => (prop) => _.get(prop.theme, key) || console.warn('missing key', key)

You can also define your own constants in a module and use those instead. For example: color: ${styleConstants.core_color}


A perk of using styled-components is that you can use it as little as you want. You can use your favorite UI framework and add styled-components on top of it. This also means that you can easily migrate an existing project component by component. You can choose to style most of the layout with standard CSS and only use styled-components for reusable components.


Designers/style integrators will need to learn very basic JavaScript to handle variables and use them in place of Sass/Less.

They will also have to learn to navigate the project structure, although I would argue that finding the styles for a component in that component’s folder is easier than having to find the right CSS/Sass/Less file that contains the rule you need to modify.

They will also need to change their tools a bit if they want syntax highlighting, linting, etc. A good place to start is with this Atom plugin and this babel plugin.


This post was written by Marcus McCurdy, Software Engineer for Toptal

Discussions criticizing Python often talk about how it is difficult to use Python for multithreaded work, pointing fingers at what is known as the global interpreter lock (affectionately referred to as the GIL) that prevents multiple threads of Python code from running simultaneously. Due to this, the Python multithreading module doesn’t quite behave the way you would expect it to if you’re not a Python developer and you are coming from other languages such as C++ or Java. It must be made clear that one can still write code in Python that runs concurrently or in parallel and make a stark difference in resulting performance, as long as certain things are taken into consideration. If you haven’t read it yet, I suggest you take a look at Eqbal Quran’s article on concurrency and parallelism in Ruby here on the Toptal Engineering Blog.

In this Python concurrency tutorial, we will write a small Python script to download the top popular images from Imgur. We will start with a version that downloads images sequentially, or one at a time. As a prerequisite, you will have to register an application on Imgur. If you do not have an Imgur account already, please create one first.

The scripts in this tutorial have been tested with Python 3.6.4. With some changes, they should also run with Python 2—urllib is what has changed the most between these two versions of Python.

Getting Started with Python Multithreading

Let us start by creating a Python module, named This file will contain all the functions necessary to fetch the list of images and download them. We will split these functionalities into three separate functions:

  • get_links
  • download_link
  • setup_download_dir

The third function, setup_download_dir, will be used to create a download destination directory if it doesn’t already exist.

Imgur’s API requires HTTP requests to bear the Authorization header with the client ID. You can find this client ID from the dashboard of the application that you have registered on Imgur, and the response will be JSON encoded. We can use Python’s standard JSON library to decode it. Downloading the image is an even simpler task, as all you have to do is fetch the image by its URL and write it to a file.

This is what the script looks like:

import json
import logging
import os
from pathlib import Path
from urllib.request import urlopen, Request

logger = logging.getLogger(__name__)

def get_links(client_id):
   headers = {'Authorization': 'Client-ID {}'.format(client_id)}
   req = Request('', headers=headers, method='GET')
   with urlopen(req) as resp:
       data = json.loads(resp.readall().decode('utf-8'))
   return map(lambda item: item['link'], data['data'])

def download_link(directory, link):'Downloading %s', link)
   download_path = directory / os.path.basename(link)
   with urlopen(link) as image,'wb') as f:

def setup_download_dir():
   download_dir = Path('images')
   if not download_dir.exists():
   return download_dir

Next, we will need to write a module that will use these functions to download the images, one by one. We will name this This will contain the main function of our first, naive version of the Imgur image downloader. The module will retrieve the Imgur client ID in the environment variable IMGUR_CLIENT_ID. It will invoke the setup_download_dir to create the download destination directory. Finally, it will fetch a list of images using the get_links function, filter out all GIF and album URLs, and then use download_link to download and save each of those images to the disk. Here is what looks like:

import logging
import os
from time import time

from download import setup_download_dir, get_links, download_link

logging.basicConfig(level=logging.DEBUG, format='%(asctime)s - %(name)s - %(levelname)s - %(message)s')
logger = logging.getLogger(__name__)

def main():
   ts = time()
   client_id = os.getenv('IMGUR_CLIENT_ID')
   if not client_id:
       raise Exception("Couldn't find IMGUR_CLIENT_ID environment variable!")
   download_dir = setup_download_dir()
   links = [l for l in get_links(client_id) if l.endswith('.jpg')]
   for link in links:
       download_link(download_dir, link)
   print('Took {}s'.format(time() - ts))

if __name__ == '__main__':

On my laptop, this script took 19.4 seconds to download 91 images. Please do note that these numbers may vary based on the network you are on. 19.4 seconds isn’t terribly long, but what if we wanted to download more pictures? Perhaps 900 images, instead of 90. With an average of 0.2 seconds per picture, 900 images would take approximately 3 minutes. For 9000 pictures it would take 30 minutes. The good news is that by introducing concurrency or parallelism, we can speed this up dramatically.

All subsequent code examples will only show import statements that are new and specific to those examples. For convenience, all of these Python scripts can be found in this GitHub repository.

Using Threads for Concurrency and Parallelism

Threading is one of the most well-known approaches to attaining Python concurrency and parallelism. Threading is a feature usually provided by the operating system. Threads are lighter than processes, and share the same memory space.

Python multithreading memory model

In our Python threading tutorial, we will write a new module to replace This module will create a pool of eight threads, making a total of nine threads including the main thread. I chose eight worker threads because my computer has eight CPU cores and one worker thread per core seemed a good number for how many threads to run at once. In practice, this number is chosen much more carefully based on other factors, such as other applications and services running on the same machine.

This is almost the same as the previous one, with the exception that we now have a new class, DownloadWorker, which is a descendent of the Python Thread class. The run method has been overridden, which runs an infinite loop. On every iteration, it calls self.queue.get() to try and fetch a URL to from a thread-safe queue. It blocks until there is an item in the queue for the worker to process. Once the worker receives an item from the queue, it then calls the same download_link method that was used in the previous script to download the image to the images directory. After the download is finished, the worker signals the queue that that task is done. This is very important, because the Queue keeps track of how many tasks were enqueued. The call to queue.join() would block the main thread forever if the workers did not signal that they completed a task.

from queue import Queue
from threading import Thread

class DownloadWorker(Thread):
   def __init__(self, queue):
       self.queue = queue

   def run(self):
       while True:
           # Get the work from the queue and expand the tuple
           directory, link = self.queue.get()
           download_link(directory, link)

def main():
   ts = time()
   client_id = os.getenv('IMGUR_CLIENT_ID')
   if not client_id:
       raise Exception("Couldn't find IMGUR_CLIENT_ID environment variable!")
   download_dir = setup_download_dir()
   links = [l for l in get_links(client_id) if l.endswith('.jpg')]
   # Create a queue to communicate with the worker threads
   queue = Queue()
   # Create 8 worker threads
   for x in range(8):
       worker = DownloadWorker(queue)
       # Setting daemon to True will let the main thread exit even though the workers are blocking
       worker.daemon = True
   # Put the tasks into the queue as a tuple
   for link in links:'Queueing {}'.format(link))
       queue.put((download_dir, link))
   # Causes the main thread to wait for the queue to finish processing all the tasks
   print('Took {}'.format(time() - ts))

Running this Python threading example script on the same machine used earlier results in a download time of 4.1 seconds! That’s 4.7 times faster than the previous example. While this is much faster, it is worth mentioning that only one thread was executing at a time throughout this process due to the GIL. Therefore, this code is concurrent but not parallel. The reason it is still faster is because this is an IO bound task. The processor is hardly breaking a sweat while downloading these images, and the majority of the time is spent waiting for the network. This is why Python multithreading can provide a large speed increase. The processor can switch between the threads whenever one of them is ready to do some work. Using the threading module in Python or any other interpreted language with a GIL can actually result in reduced performance. If your code is performing a CPU bound task, such as decompressing gzip files, using the threading module will result in a slower execution time. For CPU bound tasks and truly parallel execution, we can use the multiprocessing module.

While the de facto reference Python implementation—CPython–has a GIL, this is not true of all Python implementations. For example, IronPython, a Python implementation using the .NET framework, does not have a GIL, and neither does Jython, the Java-based implementation. You can find a list of working Python implementations here.

Related: Python Best Practices and Tips by Toptal Developers

Spawning Multiple Processes

The multiprocessing module is easier to drop in than the threading module, as we don’t need to add a class like the Python threading example. The only changes we need to make are in the main function.

Python multiprocessing tutorial: Modules

To use multiple processes, we create a multiprocessing Pool. With the map method it provides, we will pass the list of URLs to the pool, which in turn will spawn eight new processes and use each one to download the images in parallel. This is true parallelism, but it comes with a cost. The entire memory of the script is copied into each subprocess that is spawned. In this simple example, it isn’t a big deal, but it can easily become serious overhead for non-trivial programs.

from functools import partial
from multiprocessing.pool import Pool

def main():
   ts = time()
   client_id = os.getenv('IMGUR_CLIENT_ID')
   if not client_id:
       raise Exception("Couldn't find IMGUR_CLIENT_ID environment variable!")
   download_dir = setup_download_dir()
   links = [l for l in get_links(client_id) if l.endswith('.jpg')]
   download = partial(download_link, download_dir)
   with Pool(8) as p:, links)
   print('Took {}s'.format(time() - ts))

Distributing to Multiple Workers

While the threading and multiprocessing modules are great for scripts that are running on your personal computer, what should you do if you want the work to be done on a different machine, or you need to scale up to more than the CPU on one machine can handle? A great use case for this is long-running back-end tasks for web applications. If you have some long-running tasks, you don’t want to spin up a bunch of sub-processes or threads on the same machine that need to be running the rest of your application code. This will degrade the performance of your application for all of your users. What would be great is to be able to run these jobs on another machine, or many other machines.

A great Python library for this task is RQ, a very simple yet powerful library. You first enqueue a function and its arguments using the library. This pickles the function call representation, which is then appended to a Redis list. Enqueueing the job is the first step, but will not do anything yet. We also need at least one worker to listen on that job queue.

Model of the RQ Python queue library

The first step is to install and run a Redis server on your computer, or have access to a running Redis server. After that, there are only a few small changes made to the existing code. We first create an instance of an RQ Queue and pass it an instance of a Redis server from the redis-py library. Then, instead of just calling our download_link method, we call q.enqueue(download_link, download_dir, link). The enqueue method takes a function as its first argument, then any other arguments or keyword arguments are passed along to that function when the job is actually executed.

One last step we need to do is to start up some workers. RQ provides a handy script to run workers on the default queue. Just run rqworker in a terminal window and it will start a worker listening on the default queue. Please make sure your current working directory is the same as where the scripts reside in. If you want to listen to a different queue, you can run rqworker queue_name and it will listen to that named queue. The great thing about RQ is that as long as you can connect to Redis, you can run as many workers as you like on as many different machines as you like; therefore, it is very easy to scale up as your application grows. Here is the source for the RQ version:

from redis import Redis
from rq import Queue

def main():
   client_id = os.getenv('IMGUR_CLIENT_ID')
   if not client_id:
       raise Exception("Couldn't find IMGUR_CLIENT_ID environment variable!")
   download_dir = setup_download_dir()
   links = [l for l in get_links(client_id) if l.endswith('.jpg')]
   q = Queue(connection=Redis(host='localhost', port=6379))
   for link in links:
       q.enqueue(download_link, download_dir, link)

However, RQ is not the only Python job queue solution. RQ is easy to use and covers simple use cases extremely well, but if more advanced options are required, other Python 3 queue solutions (such as Celery) can be used.

Python Multithreading vs. Multiprocessing

If your code is IO bound, both multiprocessing and multithreading in Python will work for you. Multiprocessing is a easier to just drop in than threading but has a higher memory overhead. If your code is CPU bound, multiprocessing is most likely going to be the better choice—especially if the target machine has multiple cores or CPUs. For web applications, and when you need to scale the work across multiple machines, RQ is going to be better for you.


Python concurrent.futures

Something new since Python 3.2 that wasn’t touched upon in the original article is the concurrent.futurespackage. This package provides yet another way to use concurrency and parallelism with Python.

In the original article, I mentioned that Python’s multiprocessing module would be easier to drop into existing code than the threading module. This was because the Python 3 threading module required subclassing the Thread class and also creating a Queue for the threads to monitor for work.

Using a concurrent.futures.ThreadPoolExecutor makes the code almost identical to the multiprocessing module.

import logging
import os
from concurrent.futures import ThreadPoolExecutor
from functools import partial
from time import time

from download import setup_download_dir, get_links, download_link

logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(name)s - %(levelname)s - %(message)s')

logger = logging.getLogger(__name__)

def main():
    client_id = os.getenv('IMGUR_CLIENT_ID')
    if not client_id:
        raise Exception("Couldn't find IMGUR_CLIENT_ID environment variable!")
    download_dir = setup_download_dir()
    links = get_links(client_id)

    # By placing the executor inside a with block, the executors shutdown method
    # will be called cleaning up threads.
    # By default, the executor sets number of workers to 5 times the number of
    # CPUs.
    with ThreadPoolExecutor() as executor:

        # Create a new partially applied function that stores the directory
        # argument.
        # This allows the download_link function that normally takes two
        # arguments to work with the map function that expects a function of a
        # single argument.
        fn = partial(download_link, download_dir)

        # Executes fn concurrently using threads on the links iterable. The
        # timeout is for the entire process, not a single call, so downloading
        # all images must complete within 30 seconds., links, timeout=30)

if __name__ == '__main__':

Now that we have all these images downloaded with our Python ThreadPoolExecutor, we can use them to test a CPU-bound task. We can create thumbnail versions of all the images in both a single-threaded, single-process script and then test a multiprocessing-based solution.

We are going to use the Pillow library to handle the resizing of the images.

Here is our initial script.

import logging
from pathlib import Path
from time import time

from PIL import Image

logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(name)s - %(levelname)s - %(message)s')

logger = logging.getLogger(__name__)

def create_thumbnail(size, path):
    Creates a thumbnail of an image with the same name as image but with
    _thumbnail appended before the extension.  E.g.:

    >>> create_thumbnail((128, 128), 'image.jpg')

    A new thumbnail image is created with the name image_thumbnail.jpg

    :param size: A tuple of the width and height of the image
    :param path: The path to the image file
    :return: None
    image =
    path = Path(path)
    name = path.stem + '_thumbnail' + path.suffix
    thumbnail_path = path.with_name(name)

def main():
    ts = time()
    for image_path in Path('images').iterdir():
        create_thumbnail((128, 128), image_path)'Took %s', time() - ts)

if __name__ == '__main__':

This script iterates over the paths in the images folder and for each path it runs the create_thumbnail function. This function uses Pillow to open the image, create a thumbnail, and save the new, smaller image with the same name as the original but with _thumbnail appended to the name.

Running this script on 160 images totaling 36 million takes 2.32 seconds. Lets see if we can speed this up using a ProcessPoolExecutor.

import logging
from pathlib import Path
from time import time
from functools import partial

from concurrent.futures import ProcessPoolExecutor

from PIL import Image

logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(name)s - %(levelname)s - %(message)s')

logger = logging.getLogger(__name__)

def create_thumbnail(size, path):
    Creates a thumbnail of an image with the same name as image but with
    _thumbnail appended before the extension. E.g.:

    >>> create_thumbnail((128, 128), 'image.jpg')

    A new thumbnail image is created with the name image_thumbnail.jpg

    :param size: A tuple of the width and height of the image
    :param path: The path to the image file
    :return: None
    path = Path(path)
    name = path.stem + '_thumbnail' + path.suffix
    thumbnail_path = path.with_name(name)
    image =

def main():
    ts = time()
    # Partially apply the create_thumbnail method, setting the size to 128x128
    # and returning a function of a single argument.
    thumbnail_128 = partial(create_thumbnail, (128, 128))

    # Create the executor in a with block so shutdown is called when the block
    # is exited.
    with ProcessPoolExecutor() as executor:, Path('images').iterdir())'Took %s', time() - ts)

if __name__ == '__main__':

The create_thumbnail method is identical to the last script. The main difference is the creation of a ProcessPoolExecutor. The executor’s map method is used to create the thumbnails in parallel. By default, the ProcessPoolExecutor creates one subprocess per CPU. Running this script on the same 160 images took 1.05 seconds—2.2 times faster!

Async/Await (Python 3.5+ only)

One of the most requested items in the comments on the original article was for an example using Python 3’s asyncio module. Compared to the other examples, there is some new Python syntax that may be new to most people and also some new concepts. An unfortunate additional layer of complexity is caused by Python’s built-in urllib module not being asynchronous. We will need to use an async HTTP library to get the full benefits of asyncio. For this, we’ll use aiohttp.

Let’s jump right into the code and a more detailed explanation will follow.

import asyncio
import logging
import os
from time import time

import aiohttp

from download import setup_download_dir, get_links

logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(name)s - %(levelname)s - %(message)s')
logger = logging.getLogger(__name__)

async def async_download_link(session, directory, link):
    Async version of the download_link method we've been using in the other examples.
    :param session: aiohttp ClientSession
    :param directory: directory to save downloads
    :param link: the url of the link to download
    download_path = directory / os.path.basename(link)
    async with session.get(link) as response:
        with'wb') as f:
            while True:
                # await pauses execution until the 1024 (or less) bytes are read from the stream
                chunk = await
                if not chunk:
                    # We are done reading the file, break out of the while loop
                f.write(chunk)'Downloaded %s', link)

# Main is now a coroutine
async def main():
    client_id = os.getenv('IMGUR_CLIENT_ID')
    if not client_id:
        raise Exception("Couldn't find IMGUR_CLIENT_ID environment variable!")
    download_dir = setup_download_dir()
    # We use a session to take advantage of tcp keep-alive
    # Set a 3 second read and connect timeout. Default is 5 minutes
    async with aiohttp.ClientSession(conn_timeout=3, read_timeout=3) as session:
        tasks = [(async_download_link(session, download_dir, l)) for l in get_links(client_id)]
        # gather aggregates all the tasks and schedules them in the event loop
        await asyncio.gather(*tasks, return_exceptions=True)

if __name__ == '__main__':
    ts = time()
    # Create the asyncio event loop
    loop = asyncio.get_event_loop()
        # Shutdown the loop even if there is an exception
        loop.close()'Took %s seconds to complete', time() - ts)

There is quite a bit to unpack here. Let’s start with the main entry point of the program. The first new thing we do with the asyncio module is to obtain the event loop. The event loop handles all of the asynchronous code. Then, the loop is run until complete and passed the main function. There is a piece of new syntax in the definition of main: async def. You’ll also notice await and with async.

The async/await syntax was introduced in PEP492. The async def syntax marks a function as a coroutine. Internally, coroutines are based on Python generators, but aren’t exactly the same thing. Coroutines return a coroutine object similar to how generators return a generator object. Once you have a coroutine, you obtain its results with the await expression. When a coroutine calls await, execution of the coroutine is suspended until the awaitable completes. This suspension allows other work to be completed while the coroutine is suspended “awaiting” some result. In general, this result will be some kind of I/O like a database request or in our case an HTTP request.

The download_link function had to be changed pretty significantly. Previously, we were relying on urllib to do the brunt of the work of reading the image for us. Now, to allow our method to work properly with the async programming paradigm, we’ve introduced a while loop that reads chunks of the image at a time and suspends execution while waiting for the I/O to complete. This allows the event loop to loop through downloading the different images as each one has new data available during the download.

There Should Be One—Preferably Only One—Obvious Way to Do It

While the zen of Python tells us there should be one obvious way to do something, there are many ways in Python to introduce concurrency into our programs. The best method to choose is going to depend on your specific use case. The asynchronous paradigm scales better to high-concurrency workloads (like a webserver) compared to threading or multiprocessing, but it requires your code (and dependencies) to be async in order to fully benefit.

Hopefully this article—and update—will point you in the right direction so you have an idea of where to look in the Python standard library if you need to introduce concurrency into your programs.

About the Author: Marcus has a Bachelor’s in Computer Engineering and a Master’s in Computer Science. He is a talented programmer, and excels most at back-end development. However, he is comfortable creating polished products as a full stack developer.

This post was written by Amin Shah Gilani, JavaScript developer for Toptal.

I love building things—what developer doesn’t? I love thinking up solutions to interesting problems, writing implementations, and creating beautiful code. However, what I don’t like is operations. Operations is everything not involved in building great software—everything from setting up servers to getting your code shipped to production.

This is interesting, because as a freelance Ruby on Rails developer, I frequently have to create new web applications and repeat the process of figuring out the DevOps side of things. Fortunately, after creating dozens of applications, I’ve finally settled on a perfect initial deployment pipeline. Unfortunately, not everyone’s got it figured out like I have—eventually, this knowledge led me to take the plunge and document my process.

In this article, I’ll walk you through my perfect pipeline to use at the beginning of your project. With my pipeline, every push is tested, the master branch is deployed to staging with a fresh database dump from production, and versioned tags are deployed to production with back-ups and migrations happening automatically.

Note, since it’s my pipeline, it’s also opinionated and suited to my needs; however, you can feel free to swap out anything you don’t like and replace it with whatever strikes your fancy. For my pipeline, we’ll use:

  • GitLab to host code.
    • Why: My clients prefer their code to remain secret, and GitLab’s free tier is wonderful. Also, integrated free CI is awesome. Thanks GitLab!
    • Alternatives: GitHub, BitBucket, AWS CodeCommit, and many more.
  • GitLab CI to build, test, and deploy our code.
    • Why: It integrates with GitLab and is free!
    • Alternatives: TravisCI, Codeship, CircleCI, DIY with Fabric8, and many more.
  • Heroku to host our app.
    • Why: It works out of the box and is the perfect platform to start off on. You can change this in the future, but not every new app needs to run on a purpose-built Kubernetes cluster. Even Coinbase started off on Heroku.
    • Alternatives: AWS, DigitalOcean, Vultr, DIY with Kubernetes, and many more.

Old-school: Create a Basic App and Deploy It to Heroku

First, let’s recreate a typical application for someone who isn’t using any fancy CI/CD pipelines and just wants to deploy their application.

Diagram of traditional code hosting and deploying actions - pipeline

It doesn’t matter what kind of app you’re creating, but you will require Yarn or npm. For my example, I’m creating a Ruby on Rails application because it comes with migrations and a CLI, and I already have the configuration written for it. You’re welcome to use any framework or language you prefer, but you’ll need Yarn to do the versioning I do later on. I’m creating a simple CRUD app using only a few commands and no authentication.

 And let’s test if our app is running as expected. I went ahead and created a few posts, just to make sure.
The application running in development - pipeline

And let’s deploy it to Heroku by pushing our code and running migrations

$ heroku create toptal-pipeline
Creating ⬢ toptal-pipeline... done |
$ git push heroku master
Counting objects: 132, done.
 * [new branch]      master -> master
$ heroku run rails db:migrate
Running rails db:migrate on ⬢ toptal-pipeline... up, run.9653 (Free)

Finally let’s test it out in production

The application running in production

And that’s it! Typically, this is where most developers leave their operations. In the future, if you make changes, you would have to repeat the deploy and migration steps above. You may even run tests if you’re not running late for dinner. This is great as a starting point, but let’s think about this method a bit more.


  • Quick to set up.
  • Deployments are easy.


  • Not DRY: Requires repeating the same steps on every change.
  • Not versioned: “I’m rolling back yesterday’s deployment to last week’s” isn’t very specific three weeks from now.
  • Not bad-code-proof: You know you’re supposed to run tests, but no one’s looking, so you might push it despite the occasional broken test.
  • Not bad-actor-proof: What if a disgruntled developer decides to break your app by pushing code with a message about how you don’t order enough pizzas for your team?
  • Does not scale: Allowing every developer the ability to deploy would give them production level access to the app, violating the Principle of Least Privilege.
  • No staging environment: Errors specific to the production environment won’t show up until production.

The Perfect Initial Deployment Pipeline

I’m going to try something different today: Let’s have a hypothetical conversation. I’m going to give “you” a voice, and we’ll talk about how we can improve this current flow. Go ahead, say something.

Say what? Wait—I can talk?

Yes, that’s what I meant about giving you a voice. How are you?

I’m good. This feels weird

I understand, but just roll with it. Now, let’s talk about our pipeline. What’s the most annoying part about running deployments?

Oh, that’s easy. The amount of time I waste. Have you ever tried pushing to Heroku?

Yeah, watching your dependencies downloading and application being built as part of the git push is horrible!

I know, right? It’s insane. I wish I didn’t have to do that. There’s also the fact that I have to run migrations *after* deployment so I have to watch the show and check to make sure my deployment runs through

Okay, you could actually solve that latter problem by chaining the two commands with &&, like git push heroku master && heroku run rails db:migrate, or just creating a bash script and putting it in your code, but still, great answer, the time and repetition is a real pain.

Yeah, it really sucks

What if I told you you could fix that bit immediately with a CI/CD pipeline?

A what now? What is that?

CI/CD stands for continuous integration (CI) and continuous delivery/deployment (CD). It was fairly tough for me to understand exactly what it was when I was starting out because everyone used vague terms like “amalgamation of development and operations,” but put simply:

  • Continuous Integration: Making sure all your code is merged together in one place. Get your team to use Git and you’ll be using CI.
  • Continuous Delivery: Making sure your code is continuously ready to be shipped. Meaning producing read-to-distribute version of your product quickly.
  • Continuous Deployment: Seamlessly taking the product from continuous delivery and just deploying it to your servers.

Oh, I get it now. It’s about making my app magically deploy to the world!

My favorite article explaining CI/CD is by Atlassian here. This should clear up any questions you have. Anyways, back to the problem.

Yeah, back to that. How do I avoid manual deploys?

Setting Up a CI/CD Pipeline to Deploy on Push to master

What if I told you you could fix that bit immediately with a CI/CD? You can push to your GitLab remote (origin) and a computer will be spawned to straight-up simply push that code of yours to Heroku.

No way!

Yeah way! Let’s jump back into code again.

Diagram of a simple deploy CI/CD pipeline

Create a .gitlab-ci.yml with the following contents, swapping out toptal-pipeline for your Heroku app’s name:

image: ruby:2.4

  - >
   : "${HEROKU_EMAIL:?Please set HEROKU_EMAIL in your CI/CD config vars}"
  - >
   : "${HEROKU_AUTH_TOKEN:?Please set HEROKU_AUTH_TOKEN in your CI/CD config vars}"
  - curl | sh
  - |
    cat >~/.netrc <<EOF
      login $HEROKU_EMAIL
      password $HEROKU_AUTH_TOKEN
      login $HEROKU_EMAIL
      password $HEROKU_AUTH_TOKEN
  - chmod 600 ~/.netrc
  - git config --global ""
  - git config --global "CI/CD"

  APPNAME_PRODUCTION: toptal-pipeline

  stage: deploy
    name: production
    url: https://$
    - git remote add heroku$APPNAME_PRODUCTION.git
    - git push heroku master
    - heroku pg:backups:capture --app $APPNAME_PRODUCTION
    - heroku run rails db:migrate --app $APPNAME_PRODUCTION
    - master

Push this up, and watch it fail in your project’s Pipelines page. That’s because it’s missing the authentication keys for your Heroku account. Fixing that is fairly straightforward, though. First you’ll need your Heroku API key. Get it from the Manage Account page, and then add the following secret variables in your GitLab repo’s CI/CD settings:

  • HEROKU_EMAIL: The email address you use to sign into Heroku
  • HEROKU_AUTH_KEY: The key you got from Heroku
Image of the secret variables in the GitLab CI/CD settings page

This should result in a working GitLab to Heroku deploying on every push. As to what’s happening:

  • Upon pushing to master
    • The Heroku CLI is installed and authenticated in a container.
    • Your code is pushed to Heroku.
    • A backup of your database is captured in Heroku.
    • Migrations are run.

Already, you can see that not only are you saving time by automating everything to a git push, you’re also creating a backup of your database on every deploy! If anything ever goes wrong, you’ll have a copy of your database to revert back to.

Creating a Staging Environment

But wait, quick question, what happens to your production-specific problems? What if you run into a weird bug because your development environment is too different from production? I once ran into some odd SQLite 3 and PostgreSQL issues when I ran a migration. The specifics elude me, but it’s quite possible.

I strictly use PostgreSQL in development, I never mismatch database engines like that, and I diligently monitor my stack for potential incompatibilities.

Well, that’s tedious work and I applaud your discipline. Personally, I’m much too lazy to do that. However, can you guarantee that level of diligence for all potential future developers, collaborators, or contributors?

Errrr— Yeah, no. You got me there. Other people will mess it up. What’s your point, though?

My point is, you need a staging environment. It’s like production but isn’t. A staging environment is where you rehearse deploying to production and catch all your errors early. My staging environments usually mirror production, and I dump a copy of the production database on staging deploy to ensure no pesky corner cases mess up my migrations. With a staging environment, you can stop treating your users like guinea pigs.

This makes sense! So how do I do this?

Here’s where it gets interesting. I like to deploy master directly to staging.

Wait, isn’t that where we’re deploying production right now?

Yes it is, but now we’ll be deploying to staging instead.

But if master deploys to staging, how do we deploy to production?

By using something you should’ve been doing years ago: Versioning our code and pushing Git tags.

Git tags? Who uses Git tags?! This is beginning to sound like a lot of work.

It sure was, but thankfully, I’ve done all that work already and you can just just dump my code and it’ll work.

Overview of how staging and production deploys will work

First, add a block about the staging deploy to your .gitlab-ci.yml file, I’ve created a new Heroku app called toptal-pipeline-staging:

  APPNAME_PRODUCTION: toptal-pipeline
  APPNAME_STAGING: toptal-pipeline-staging

  stage: deploy
    name: staging
    url: https://$
    - git remote add heroku$APPNAME_STAGING.git
    - git push heroku master
    - heroku pg:backups:capture --app $APPNAME_PRODUCTION
    - heroku pg:backups:restore `heroku pg:backups:url --app $APPNAME_PRODUCTION` --app $APPNAME_STAGING --confirm $APPNAME_STAGING
    - heroku run rails db:migrate --app $APPNAME_STAGING
    - master
    - tags


Then change the last line of your production block to run on semantically versioned Git tags instead of the master branch:

    - /^v(?'MAJOR'(?:0|(?:[1-9]\d*)))\.(?'MINOR'(?:0|(?:[1-9]\d*)))\.(?'PATCH'(?:0|(?:[1-9]\d*)))(?:-(?'prerelease'[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*))?(?:\+(?'build'[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*))?$/
    # semver pattern above is adapted from

Running this right now will fail because GitLab is smart enough to only allow “protected” branches access to our secret variables. To add version tags, go to your GitLab project’s repository settings page and add v* to protected tags.

Image of the version tag being added to protected tags in the repository settings page

Let’s recap what’s happening now:

  • Upon pushing to master, or pushing a tagged commit
    • The Heroku CLI is installed and authenticated in a container.
    • Your code is pushed to Heroku.
    • A backup of your database production is captured in Heroku.
    • The backup is dumped in your staging environment.
    • Migrations are run on the staging database.
  • Upon pushing a semantically version tagged commit
    • The Heroku CLI is installed and authenticated in a container.
    • Your code is pushed to Heroku.
    • A backup of your database production is captured in Heroku.
    • Migrations are run on the production database.

Do you feel powerful now? I feel powerful. I remember, the first time I came this far, I called my wife and explained this entire pipeline in excruciating detail. And she’s not even technical. I was super impressed with myself, and you should be too! Great job coming this far!

Testing Every Push

But there’s more, since a computer’s doing stuff for you anyways, it could also run all the things you’re too lazy to do: Tests, linting errors, pretty much anything you want to do, and if any of these fail, they won’t move on to deployment.

I love having this in my pipeline, it makes my code reviews fun. If a merge request gets through all my code-checks, it deserves to be reviewed.

Image of Testing on every push

Add a test block:

  stage: test
    POSTGRES_PASSSWORD: test-password
    POSTGRES_DB: test
    RAILS_ENV: test
    - postgres:alpine
    - curl -sL | bash
    - apt-get update -qq && apt-get install -yqq nodejs libpq-dev
    - curl -o- -L | bash
    - source ~/.bashrc
    - yarn
    - gem install bundler  --no-ri --no-rdoc
    - bundle install -j $(nproc) --path vendor
    - bundle exec rake db:setup RAILS_ENV=test
    - bundle exec rake spec
    - bundle exec rubocop

Let’s recap what’s happening now:

  • Upon every push, or merge request
    • Ruby and Node are set up in a container.
    • Dependencies are installed.
    • The app is tested.
  • Upon pushing to master, or pushing a tagged commit, and only if all tests pass
    • The Heroku CLI is installed and authenticated in a container.
    • Your code is pushed to Heroku.
    • A backup of your database production is captured in Heroku.
    • The backup is dumped in your staging environment.
    • Migrations are run on the staging database.
  • Upon pushing a semantically version tagged commit, and only if all tests pass
    • The Heroku CLI is installed and authenticated in a container.
    • Your code is pushed to Heroku.
    • A backup of your database production is captured in Heroku.
    • Migrations are run on the production database.

Take a step back and marvel at the level of automation you’ve accomplished. From now on, all you have to do is write code and push. Test out your app manually in staging if you feel like it, and when you feel confident enough to push it out to the world, tag it with semantic versioning!

Automatic Semantic Versioning

Yeah, it’s perfect, but there’s something missing. I don’t like looking up the last version of the app and explicitly tagging it. That takes multiple commands and distracts me for a few seconds.

Okay, dude, stop! That’s enough. You’re just over-engineering it now. It works, it’s brilliant, don’t ruin a good thing by going over the top.

Okay, I have a good reason for doing what I’m about to do.

Pray, enlighten me.

I used to be like you. I was happy with this setup, but then I messed up. git tag lists tags in alphabetical order, v0.0.11 is above v0.0.2. I once accidentally tagged a release and continued doing it for about half a dozen releases until I saw my mistake. That’s when I decided to automate this too.

Here we go again

Okay, so, thankfully, we have the power of npm at our disposal, so I found a suitable package: Run yarn add --dev standard-version and add the following to your package.json file:

  "scripts": {
    "release": "standard-version",
    "major": "yarn release --release-as major",
    "minor": "yarn release --release-as minor",
    "patch": "yarn release --release-as patch"

Now you need to do one last thing, configure Git to push tags by default. At the moment, you need to run git push --tags to push a tag up, but automatically doing that on regular git push is as simple as running git config --global push.followTags true.

To use your new pipeline, whenever you want to create a release run:

  • yarn patch for patch releases
  • yarn minor for minor releases
  • yarn major for major releases

If you’re unsure about what the words “major,” “minor,” and “patch” mean, read more about this at the semantic versioning site.

Now that you’ve finally completed your pipeline, let’s recap how to use it!

  • Write code.
  • Commit and push it to test and deploy it to staging.
  • Use yarn patch to tag a patch release.
  • git push to push it out to production.

Summary and Further Steps

I’ve only just scratched the surface of what’s possible with CI/CD pipelines. This is a fairly simplistic example. You can do so much more by swapping out Heroku with Kubernetes. If you decide to use GitLab CI read the yaml docs because there’s so much more you can do by caching files between deploys, or saving artifacts!

Another huge change you could make to this pipeline is introduce external triggers to run the semantic versioning and releasing. Currently, ChatOps is part of their paid plan, and I hope they release it to free plans. But imagine being able to trigger the next image through a single Slack command!

Diagram of a CI/CD deployment pipeline where production deploys are triggered externally, possibly via chat or webhooks

Eventually, as your application starts to grow complex and requires system level dependencies, you may need to use a container. When that happens, check out our guide: Getting Started with Docker: Simplifying Devops .

This example app really is live, and you can find the source code for it here.

This post was written by Phillip Brennan, Software Developer for Toptal.

Regardless of the apparent evidence to the contrary, programming employees are humans. And, as all humans, we like taking advantage over our freedom of choice. Whether that choice is about taking the red pill or the blue pill, wearing a dress or pants, or using one development environment over another, the choice we make places us in one group of people or another. Choice, inevitably, comes after our evaluation of options. And having made a choice, we tend to believe that anyone who chooses differently made a mistake.

You can easily search the internet and find hundreds of debates about Emacs vs Vim. Even if you read them all, it will be impossible to objectively choose a winner. However, does the choice of development environment tell you anything about the quality of work a developer can deliver? Absolutely not!

great developer could write her code into Notepad and still deliver great stuff.

Certainly, there are a lot of things professionals consider when selecting tools for their work. This is true for every profession, including software development. Quite often, however, selection is based on personal taste, not something easily tangible.

Programmers spend most of their time looking at the development environment, so it is natural that we want something pretty as well as functional. Every development environment has its pros and cons. As a whole, they a driving force of the software development industry.

best programming editors

What are the things a developer should evaluate when choosing a set of programming tools like a programming editor of choice? The answer to this question is not as simple as it might sound. Software development is close to an art, and there are quite few “fuzzy” factors that separate a masterpiece from an overpriced collectable.

Every programming language, be it Java, C#, PHP, Python, Ruby, JavaScript, and so on, has its own development practices related to project structure, debugging, and deploying. However, one thing they all have in common is editing code. In this article we will evaluate different development platforms from the perspective of the most common task in software development: writing code.

IDE vs General Purpose Text Editor

An integrated development environment (IDE) (or interactive development environment) is a software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of a source code editor, build automation tools, and a debugger, and many support lots of additional plugins and extensions.

Text editors are simpler applications. Compared to IDEs, they usually correspond to just the code editor segment of an IDE. However, they are often much more than that. IDEs are created to serve the purpose of software development, while many text editors are designed to be used by non-developers as well.

Static-typed languages can get a lot of benefits from IDEs. Because of the strict typing rules, it is possible for the IDE to detect bugs and naming inconsistencies across classes and modules, and even across files, directly in the editor, before compiling. This functionality comes standard with many IDEs, and for that reason, IDEs are very popular for static-typed languages.

However, it is impossible to do the same thing for dynamically typed languages. For example, if a method name may be generated by the code itself, constructed from a series of string concats, trying to detect naming errors in dynamic languages requires nothing less than running the actual program. Because one of the major benefits of IDEs does not apply to dynamic language programmers, they have a greater tendency to stick with text editors like Sublime. As a side note, this is also a major reason why the test-driven development movement has grown up around dynamic language communities, and has not had as strong of a following in static languages.

What Makes a Great Programming Editor?

Aside from a number of different features for various languages, every programming editor needs to have a well-organized and clean user interface. Overall aesthetic appeal should not be overlooked, either. It is not just a matter of looking good, as a well-designed editor with the right choice of font and colors helps keep eyestrain down and lets you be more productive.

In today’s development environment, a steep learning curve is a liability, regardless of feature set. Time is always valuable, so a good editor should be easy to get used to. Ideally, the programmer should be able to start work immediately, without having to jump through too many hoops. A Swiss army knife is a practical and useful tool, yet anyone can master it in minutes. Likewise, for programming editors, simplicity is a virtue.

User Interface, Features, and Workflow

Let’s take a closer look at UI, different features and capabilities, and frequently used tools that should be a part of any programming editor.

Line numbers, of course, should be on by default and simple to turn on or off.

Snippets are useful for inserting standardized blocks of text in a fixed layout. However, programming is a lot about saying things just once, so be careful with snippets as they might make your code hard to maintain in the future.

The ability to lint, or syntax-check, the current file is useful, as is the ability to launch it. Without this facility, a programmer must switch to an external command line window, choose and run the correct command, and then step through error messages to find the source of the error. However, the linting must be under the programmer’s control, because the delay incurred by the lint might interrupt the coder at a crucial moment.

inline doc

Inline doc is useful as long as it does not get in the way, but having a browser page open on the class definitions is sometimes more useful, especially when there are lots of related classes that do not directly extend each other. It is easy enough to cut and paste code from the browser documentation to the code being written, so the additional complexity of inline documentation often becomes less useful, indeed, more annoying, as the programmer’s knowledge of the documentation increases.

Word-completion is helpful since it is fast, and almost as reliable as in-edit documentation, while being less intrusive. It is satisfying to enter just a few characters of a word and then hit enter to get the rest. Otherwise, one labors under the strain of excess typing, abhorred by lazy programmers, who want to type ee rather than the more lengthy exponentialFunctionSquared. Word completion satisfies by minimizing typing, enforcing coherent naming and by not getting in the way.

Renaming variables and functions across the program is useful, but you need to be able to review changes and make sure your code is not broken. Again, word completion is a useful halfway house, in that it works for all languages; you can use long names for items that have long lifetimes, without incurring a typing overhead. You can use references to them via a shorter name locally, in order to shorten expressions which might otherwise spread over too many lines. If you need to rename, the long names are unique, so this approach works across all languages, and all files.

Source files can sometimes grow a lot. Code-folding is a nice feature that simplifies reading through long files.

Find/change with scope limitation to local, incremental, or global with meta characters and regular expressions are part of the minimum requirement these days, as is syntax highlighting.

Over the years, I went through a number of editors, and this is what I think of them:

  • Emacs: One of the most popular editors in the world. Emacs’ greatest feature is its extensibility, despite the complexity of its extension language (you can even play Tetris in it with M-x tetris). Emacs fans consider its terminal-based interface to be a great feature, while others might debate that it’s a drawback. In my personal experience, I found it too much to adopt and learn. I am sure that if you know how to use Emacs you will never use anything else, but to take on and learn the entire culture was more than I wanted to do. Nevertheless, its popularity among developers proves that it is far from being a relic of the old times, and remains part of our future as well.
  • Vi/Vim: Vim is another powerful terminal-based editor, and it comes standard with most xNIX operating systems. Apart from having a different interface than Emacs, my view is practically the same. If you grew up on it, I am sure you will never use anything else. Having Vi skills will make your life much simpler when operating through SSH and other tight spots, and you wont have problems with speed, once you get familiar with keystrokes. While not as tough to crack into as Emacs, the learning curve is still quite steep, and it could definitely use few nice features of a windowed editor.
  • SublimeText: True to its name, SublimeText is a beautiful text editor with tons of features. Unlike some similar editors, SublimeText is closed source, so it cannot be modified at a low level. SublimeText offers the simplicity of traditional text editors, with a lean and fast UI. Many developers find it easier to use than Vim, and this is especially true of newcomers. The learning curve just isn’t as steep. While the UI is minimal and straightforward, SublimeText does offer a few nifty features, such as a scaled down display code on the right of the UI, allowing users to quickly scroll through their code and navigate with relative ease. While it’s not completely free, the feature-limited demo version is. Unlocking all the features will cost you $70.
  • Atom is the result of a GitHub effort to produce a programming editor for a new generation of developers. While it is still a work in progress, Atom is a very capable editor with a vibrant community of developers keen on new extensions, JavaScript libraries and more. It’s downsides include some UI quirks, the possibility that some add-on packages could misbehave, and reported performance issues when working with (very) big files. But the project is under active development, and current shortcomings are likely to be improved. Atom is an open source project, and it can easily be hacked to suit your needs.
  • Nano: Excellent in a tight corner, but not feature-rich enough to prevent the inevitable thought creeping into one’s mind that there must be faster way to do this as one struggles through the keystrokes to indent a block of code, while keeping the comments lined up in column 80! It does not even have text highlighting, and should not be used for anything more than config file changes.
  • TextMate2: TextMate’s biggest drawback is that it only runs on Mac. As its creators put it, “TextMate brings Apple’s approach to operating systems into the world of text editors.” By bridging UNIX underpinnings and GUI, TextMate cherry-picks the best of both worlds, to the benefit of expert scripters and novice users alike. It is the editor of choice for many Ruby, Python, and JavaScript developers, with great support for Bash or Markdown as well. At the moment of publishing this article TextMate 2 is still in Beta, but it already has a very mature plugin ecosystem that promises to extend it even beyond Emacs’s extensions.
  • jEdit: Java-based, and considered slow by some. Out of the box configuration might push certain people away, but jEdit can be extremely fast if configured properly, as well as extremely nice looking.
  • Eclipse: Another widely used IDE, Eclipse is very popular among Java developers, but has been adapted to many different platforms. We could argue that its monolithic architecture is a rock that will pull it under the water, but it is still one of the most popular platforms among developers.
  • Aptana Studio: A comprehensive open-source web application IDE. It is available as an Eclipse plugin, which makes it popular among some Java developers. The standalone version is even leaner, and offers a range of different themes and customization options. Aptana’s project management capabilities may also come in handy to coders who honed their skills in Eclipse. While earlier versions suffered from performance issues on some hardware platforms, these problems were addressed in Aptana Studio 3, and should be a thing of the past.
  • NetBeans: Another relatively popular open-source IDE with cross-platform support. It is somewhat slower on startup than lean editors like SublimeText, and the choice of add-ons is limited compared to some alternatives. Many Java developers have grown to love NetBeans thanks to seamless SCM integration and HTML5 support. NetBeans support for PHP has also improved in the latest releases.
  • JetBrains: Offers a family of IDEs for Java, Ruby, Python and PHP. They are all based on the same core engine. Very capable in its own right, JetBrains IDEs have been gaining a growing following. However, they are not free, open-source solutions, although a 30-day trial is available, and pricing is reasonable.
  • Komodo Edit: Komodo Edit has great potential, and yet it’s full of annoying little “gotchas” and idiosyncrasies that can be frustrating by its lack of orthogonality. Komodo Edit feels cluttered, which is a shame because it clearly has immense capability. I keep going back to Komodo Edit in the hopes that I have missed some organizing principle, and every time, I am beaten back by a welter of disorganized capability.
  • Geany: Geany is not a major power player like many of the other editors in this list. It is defined more by “what it is not” than “what it is.” It is not slow, it does not have a lot of heritage from the old days, it does not have a macro capability, or much of a multi window on buffer capability. Yet the things it does do, it does well enough. It is, perhaps, the least demanding of all the editors that I tried and still can do 90 percent of what you would expect from a programmer’s editor. Geany looks good enough on Ubuntu, which is one of the reason I chose it as my preferred editor.

My Conclusion

It would be presumptuous to declare just one as the best programming editor among these great tools. And there are quite a few editors I did not even try. There is no one-size-fits-all solution. This is what compelled me to try out a number of different editors.

I currently am using Geany, but it’s because it fits the requirements I have. With Geany, and a lot of help from Perl/Gimp/Audacity/Sox, I am able to develop and maintain the Java code-base for the Android apps I develop, prepare them for compilation in different configurations for multiple distributors, source, lint, compile, dex and produce .apk files, and deliver these apps globally.

Your line of development might set a different set of requirements, and I hope I saved you some time in researching for the most appropriate programming editors.

This post was written by Federico Pereiro, JavaScript Developer for Toptal.

Declarative programming is, currently, the dominant paradigm of an extensive and diverse set of domains such as databases, templating and configuration management.

In a nutshell, declarative programming consists of instructing a program on what needs to be done, instead of telling it how to do it. In practice, this approach entails providing a domain-specific language (DSL) for expressing what the user wants, and shielding them from the low-level constructs (loops, conditionals, assignments) that materialize the desired end state.

While this paradigm is a remarkable improvement over the imperative approach that it replaced, I contend that declarative programming has significant limitations, limitations that I explore in this article. Moreover, I propose a dual approach that captures the benefits of declarative programming while superseding its limitations.

CAVEATThis article emerged as the result of a multi-year personal struggle with declarative tools. Many of the claims I present here are not thoroughly proven, and some are even presented at face value. A proper critique of declarative programming would take considerable time, effort, and I would have to go back and use many of these tools; my heart is not in such an undertaking. The purpose of this article is to share a few thoughts with you, pulling no punches, and showing what worked for me. If you’ve struggled with declarative programming tools, you might find respite and alternatives. And if you enjoy the paradigm and its tools, don’t take me too seriously.

If declarative programming works well for you, I’m in no position to tell you otherwise.

You can love or hate declarative programming, but you cannot afford to ignore it.
You can love or hate declarative programming, but you cannot afford to ignore it.

The Merits Of Declarative Programming

Before we explore the limits of declarative programming, it is necessary to understand its merits.

Arguably the most successful declarative programming tool is the relational database (RDB). It might even be the first declarative tool. In any case, RDBs exhibit the two properties that I consider archetypical of declarative programming:

  • A domain specific language (DSL): the universal interface for relational databases is a DSL named Structured Query Language, most commonly known as SQL.
  • The DSL hides the lower level layer from the user: ever since Edgar F. Codd’s original paper on RDBs, it is plain that the power of this model is to dissociate the desired queries from the underlying loops, indexes and access paths that implement them.

Before RDBs, most database systems were accessed through imperative code, which is heavily dependent on low-level details such as the order of records, indexes and the physical paths to the data itself. Because these elements change over time, code often stops working because of some underlying change in the structure of the data. The resulting code is hard to write, hard to debug, hard to read and hard to maintain. I’ll go out a limb and say that most of this code was in, all likelihood, long, full of proverbial rats’ nests of conditionals, repetition and subtle, state-dependent bugs.

In the face of this, RDBs provided a tremendous productivity leap for systems developers. Now, instead of thousands of lines of imperative code, you had a clearly defined data scheme, plus hundreds (or even just tens) of queries. As a result, applications had only to deal with an abstract, meaningful and lasting representation of data, and interface it through a powerful, yet simple query language. The RDB probably raised the productivity of programmers, and companies that employed them, by an order of magnitude.

What are the commonly listed advantages of declarative programming?

Proponents of declarative programming are quick to point out the advantages. However, even they admit it comes with trade-offs.
Proponents of declarative programming are quick to point out the advantages. However, even they admit it comes with trade-offs.
  1. Readability/usability: a DSL is usually closer to a natural language (like English) than to pseudocode, hence more readable and also easier to learn by non-programmers.
  2. Succinctness: much of the boilerplate is abstracted by the DSL, leaving less lines to do the same work.
  3. Reuse: it is easier to create code that can be used for different purposes; something that’s notoriously hard when using imperative constructs.
  4. Idempotence: you can work with end states and let the program figure it out for you. For example, through an upsert operation, you can either insert a row if it is not there, or modify it if it is already there, instead of writing code to deal with both cases.
  5. Error recovery: it is easy to specify a construct that will stop at the first error instead of having to add error listeners for every possible error. (If you’ve ever written three nested callbacks in node.js, you know what I mean.)
  6. Referential transparency: although this advantage is commonly associated with functional programming, it is actually valid for any approach that minimizes manual handling of state and relies on side effects.
  7. Commutativity: the possibility of expressing an end state without having to specify the actual order in which it will be implemented.

While the above are all commonly cited advantages of declarative programming, I would like to condense them into two qualities, which will serve as guiding principles when I propose an alternative approach.

  1. A high-level layer tailored to a specific domain: declarative programming creates a high-level layer using the information of the domain to which it applies. It is clear that if we’re dealing with databases, we want a set of operations for dealing with data. Most of the seven advantages above stem from the creation of a high-level layer that is precisely tailored to a specific problem domain.
  2. Poka-yoke (fool-proofness): a domain-tailored high-level layer hides the imperative details of the implementation. This means that you commit far fewer errors because the low-level details of the system are simply not accessible. This limitation eliminates many classes of errors from your code.

Two Problems With Declarative Programming

In the following two sections, I will present the two main problems of declarative programming: separateness and lack of unfolding. Every critique needs its bogeyman, so I will use HTML templating systems as a concrete example of the shortcomings of declarative programming.

The Problem With DSLs: Separateness

Imagine that you need to write a web application with a non-trivial number of views. Hard coding these views into a set of HTML files is not an option because many components of these pages change.

The most straightforward solution, which is to generate HTML by concatenating strings, seems so horrible that you will quickly look for an alternative. The standard solution is to use a template system. Although there are different types of template systems, we will sidestep their differences for the purpose of this analysis. We can consider all of them to be similar in that the main mission of template systems is to provide an alternative to code that concatenates HTML strings using conditionals and loops, much like RDBs emerged as an alternative to code that looped through data records.

Let’s suppose we go with a standard templating system; you will encounter three sources of friction, which I will list in ascending order of importance. The first is that the template necessarily resides in a file separate from your code. Because the templating system uses a DSL, the syntax is different, so it cannot be in the same file. In simple projects, where file counts are low, the need to keep separate template files may duplicate or treble the amount of files.

I open an exception for Embedded Ruby templates (ERB), because those are integrated into Ruby source code. This is not the case for ERB-inspired tools written in other languages since those templates must also be stored as different files.

The second source of friction is that the DSL has its own syntax, one different from that of your programming language. Hence, modifying the DSL (let alone writing your own) is considerably harder. To go under the hood and change the tool, you need to learn about tokenizing and parsing, which is interesting and challenging, but hard. I happen to see this as a disadvantage.

How can one vizualise a DSL? It’s not easy, but let’s just say a DSL is a clean, shiny layer on top of low-level constructs.
How can one vizualise a DSL? It’s not easy, but let’s just say a DSL is a clean, shiny layer on top of low-level constructs.

You may ask, “Why on earth would you want to modify your tool? If you are doing a standard project, a well-written standard tool should fit the bill.” Maybe yes, maybe no.

A DSL never has the full power of a programming language. If it did, it wouldn’t be a DSL anymore, but rather a full programming language.

But isn’t that the whole point of a DSL? To not have the full power of a programming language available, so that we can achieve abstraction and eliminate most sources of bugs? Maybe, yes. However, most DSLs start simple and then gradually incorporate a growing number of the facilities of a programming language until, in fact, it becomes one. Template systems are a perfect example. Let’s see the standard features of template systems and how they correlate to programming language facilities:

  • Replace text within a template: variable substitution.
  • Repetition of a template: loops.
  • Avoid printing a template if a condition is not met: conditionals.
  • Partials: subroutines.
  • Helpers: subroutines (the only difference with partials is that helpers can access the underlying programming language and let you out of the DSL straightjacket).

This argument, that a DSL is limited because it simultaneously covets and rejects the power of a programming language, is directly proportional to the extent that the features of the DSL are directly mappable to the features of a programming language. In the case of SQL, the argument is weak because most of the things SQL offers are nothing like what you find in a normal programming language. At the other end of the spectrum, we find template systems where virtually every feature is making the DSL converge towards BASIC.

Let’s now step back and contemplate these three quintessential sources of friction, summed up by the concept of separateness. Because it is separate, a DSL needs to be located on a separate file; it is harder to modify (and even harder to write your own), and (often, but not always) needs you to add, one by one, the features you miss from a real programming language.

Separateness is an inherent problem of any DSL, no matter how well designed.

We now turn to a second problem of declarative tools, which is widespread but not inherent.

Another Problem: Lack Of Unfolding Leads To Complexity

If I had written this article a few months ago, this section would have been named Most Declarative Tools Are #@!$#@! Complex But I Don’t Know Why. In the process of writing this article I found a better way of putting it: Most Declarative Tools Are Way More Complex Than They Need To Be. I will spend the rest of this section explaining why. To analyze the complexity of a tool, I propose a measure called the complexity gap. The complexity gap is the difference between solving a given problem with a tool versus solving it in the lower level (presumably, plain imperative code) that the tool intends to replace. When the former solution is more complex than the latter, we are in presence of the complexity gap. By more complex, I mean more lines of code, code that’s harder to read, harder to modify and harder to maintain, but not necessarily all of these at the same time.

Please note that we’re not comparing the lower level solution against the best possible tool, but rather against no tool. This echoes the medical principle of “First, do no harm”.

Signs of a tool with a large complexity gap are:

  • Something that takes a few minutes to describe in rich detail in imperative terms will take hours to code using the tool, even when you know how to use the tool.
  • You feel you are constantly working around the tool rather than with the tool.
  • You are struggling to solve a straightforward problem that squarely belongs in the domain of the tool you are using, but the best Stack Overflow answer you find describes a workaround.
  • When this very straightforward problem could be solved by a certain feature (which does not exist in the tool) and you see a Github issue in the library that features a long discussion of said feature with +1s interspersed.
  • A chronic, itching, longing to ditch the tool and do the whole thing yourself inside a _ for- loop_.

I might have fallen prey to emotion here since template systems are not that complex, but this comparatively small complexity gap is not a merit of their design, but rather because the domain of applicability is quite simple (remember, we’re just generating HTML here). Whenever the same approach is used for a more complex domain (such as configuration management) the complexity gap may quickly turn your project into a quagmire.

That said, it is not necessarily unacceptable for a tool to be somewhat more complex than the lower level it intends to replace; if the tool yields code that is more readable, concise and correct, it can be worth it t. It’s an issue when the tool is several times more complex than the problem it replaces; this is flat-out unacceptable. Brian Kernighan famously stated that, “Controlling complexity is the essence of computer programming.” If a tool adds significant complexity to your project, why even use it?

The question is, why are some declarative tools so much more complex than they need be? I think it would be a mistake to blame it on poor design. Such a general explanation, a blanket ad-hominem attack on the authors of these tools, is not fair. There has to be a more accurate and enlightening explanation.

Origami time! A tool with a high-level interface to an abstract lower level has to unfold the higher level from the lower one.
Origami time! Origami time! A tool with a high-level interface to an abstract lower level has to unfold the higher level from the lower one.

My contention is that any tool that offers a high level interface to abstract a lower level must unfold this higher level from the lower one. The concept of unfolding comes from Christopher Alexander’s magnum opus, The Nature of Order – in particular Volume II. It is (hopelessly) beyond the scope of this article (not to mention my understanding) to summarize the implications of this monumental work for software design; I believe its impact will be huge in years to come. It is also beyond this article to provide a rigorous definition of unfolding processes. I will use here the concept in a heuristic way.

An unfolding process is one that, in a stepwise fashion, creates further structure without negating the existing one. At every step, each change (or differentiation, to use Alexander’s term) remains in harmony with any previous structure, when previous structure is, simply, a crystallized sequence of past changes.

Interestingly enough, Unix is a great example of the unfolding of a higher level from a lower one. In Unix, two complex features of the operative system, batch jobs and coroutines (pipes), are simply extensions of basic commands. Because of certain fundamental design decisions, such as making everything a stream of bytes, the shell being a userland programand standard I/O files, Unix is able to provide these sophisticated features with minimal complexity.

To underline why these are excellent examples of unfolding, I would like to quote a few excerpts of a 1979 paper by Dennis Ritchie, one of the authors of Unix:

On batch jobs:

… the new process control scheme instantly rendered some very valuable features trivial to implement; for example detached processes (with &) and recursive use of the shell as a command. Most systems have to supply some sort of special batch job submissionfacility and a special command interpreter for files distinct from the one used interactively.

On coroutines:

The genius of the Unix pipeline is precisely that it is constructed from the very same commands used constantly in simplex fashion.

UNIX pioneers Dennis Ritchie and Ken Thompson created a powerful demonstration of unfolding in their OS. They also saved us from a dystopian all-Windows future.
UNIX pioneers Dennis Ritchie and Ken Thompson created a powerful demonstration of unfolding in their OS. They also saved us from a dystopian all-Windows future.

This elegance and simplicity, I argue, comes from an unfolding process. Batch jobs and coroutines are unfolded from previous structures (commands run in a userland shell). I believe that because of the minimalist philosophy and limited resources of the team that created Unix, the system evolved stepwise, and as such, was able to incorporate advanced features without turning its back on to the basic ones because there weren’t enough resources to do otherwise.

In the absence of an unfolding process, the high level will be considerably more complex than necessary. In other words, the complexity of most declarative tools stem from the fact that their high level does not unfold from the low level they intend to replace.

This lack of unfoldance, if you forgive the neologism, is routinely justified by the necessity to shield the user from the lower level. This emphasis on poka-yoke (protecting the user from low level errors) comes at the expense of a large complexity gap that is self-defeating because the extra complexity will generate new classes of errors. To add insult to injury, these classes of errors have nothing to do with the problem domain but rather with the tool itself. We would not go too far if we describe these errors as iatrogenic.

Declarative templating tools, at least when applied to the task of generating HTML views, are an archetypical case of a high level that turns its back on the low level it intends to replace. How so? Because generating any non-trivial view requires logic, and templating systems, especially logic-less ones, banish logic through the main door and then smuggle some of it back through the cat door.

Note: An even weaker justification for a large complexity gap is when a tool is marketed as magic, or something that just works, the opaqueness of the low level is supposed to be an asset because a magic tool is always supposed to work without you understanding why or how. In my experience, the more magical a tool purports to be, the faster it transmutes my enthusiasm into frustration.

But what about the separation of concerns? Shouldn’t view and logic remain separate? The core mistake, here, is to put business logic and presentation logic in the same bag. Business logic certainly has no place in a template, but presentation logic exists nevertheless. Excluding logic from templates pushes presentation logic into the server where it is awkwardly accommodated. I owe the clear formulation of this point to Alexei Boronine, who makes an excellent case for it in this article.

My feeling is that roughly two thirds of the work of a template resides in its presentation logic, while the other third deals with generic issues such as concatenating strings, closing tags, escaping special characters, and so on. This is the two-faced low level nature of generating HTML views. Templating systems deal appropriately with the second half, but they don’t fare well with the first. Logic-less templates flat out turn their back on this problem, forcing you to solve it awkwardly. Other template systems suffer because they truly need to provide a non-trivial programming language so their users can actually write presentation logic.

To sum up; declarative templating tools suffer because:

  • If they were to unfold from their problem domain, they would have to provide ways to generate logical patterns;
  • A DSL that provides logic is not really a DSL, but a programming language. Note that other domains, like configuration management, also suffer from lack of “unfoldance.”

I would like to close the critique with an argument that is logically disconnected from the thread of this article, but deeply resonates with its emotional core: We have limited time to learn. Life is short, and on top of that, we need to work. In the face of our limitations, we need to spend our time learning things that will be useful and withstand time, even in the face of fast changing technology. That is why I exhort you to use tools that don’t just provide a solution but actually shed a bright light on the domain of its own applicability. RDBs teach you about data, and Unix teaches you about OS concepts, but with unsatisfactory tools that don’t unfold, I’ve always felt I was learning the intricacies of a sub-optimal solution while remaining in the dark about the nature of problem it intends to solve.

The heuristic I suggest you to consider is, value tools that illuminate their problem domain, instead of tools that obscure their problem domain behind purported features.

The Twin Approach

To overcome the two problems of declarative programming, which I have presented here, I propose a twin approach:

  • Use a data structure domain specific language (dsDSL), to overcome separateness.
  • Create a high level that unfolds from the lower level, to overcome the complexity gap.


A data structure DSL (dsDSL) is a DSL that is built with the data structures of a programming language. The core idea is to use the basic data structures you have available, such as strings, numbers, arrays, objects and functions, and combine them to create abstractions to deal with a specific domain.

We want to keep the power of declaring structures or actions (high level) without having to specify the patterns that implement these constructs (low level). We want to overcome the separateness between the DSL and our programming language so that we are free to use the full power of a programming language whenever we need it. This is not only possible but straightforward through dsDSLs.

If you asked me a year ago, I would have thought that the concept of dsDSL was novel, then one day, I realized that JSON itself was a perfect example of this approach! A parsed JSON object consists of data structures that declaratively represent data entries in order to get the advantages of the DSL while also making it easy to parse and handle from within a programming language. (There might be other dsDSLs out there, but so far I haven’t come across any. If you know of one, I would really appreciate your mentioning it in the comments section.)

Like JSON, a dsDSL has the following attributes:

  1. It consists of a very small set of functions: JSON has two main functions, parse and stringify.
  2. Its functions most commonly receive complex and recursive arguments: a parsed JSON is an array, or object, which usually contains further arrays and objects inside.
  3. The inputs to these functions conform to very specific forms: JSON has an explicit and strictly enforced validation schema to tell valid from invalid structures.
  4. Both the inputs and the outputs of these functions can be contained and generated by a programming language without a separate syntax.

But dsDSLs go beyond JSON in many ways. Let’s create a dsDSL for generating HTML using Javascript. Later I will touch on the issue of whether this approach may be extended to other languages (spoiler: It can definitely be done in Ruby and Python, but probably not in C).

HTML is a markup language composed of tags delimited by angle brackets (< and >). These tags may have optional attributes and contents. Attributes are simply a list of key/value attributes, and contents may be either text or other tags. Both attributes and contents are optionals for any given tag. I’m simplifying somewhat, but it is accurate.

A straightforward way to represent an HTML tag in a dsDSL is by using an array with three elements: – Tag: a string. – Attributes: an object (of the plain, key/value type) or undefined (if no attributes are necessary). – Contents: a string (text), an array (another tag) or undefined (if there’s no contents).

For example, <a href="views">Index</a> can be written as ['a', {href: 'views'}, 'Index'].

If we want to embed this anchor element into a div with class links, we can write: ['div', {class: 'links'}, ['a', {href: 'views'}, 'Index']].

To list several html tags at the same level, we can wrap them in an array:

   ['h1', 'Hello!'],
   ['a', {href: 'views'}, 'Index']

The same principle may be applied to creating multiple tags within a tag:

['body', [
   ['h1', 'Hello!'],
   ['a', {href: 'views'}, 'Index']

Of course, this dsDSL won’t get us far if we don’t generate HTML from it. We need a generate function which will take our dsDSL and yield a string with HTML. So if we run generate (['a', {href: 'views'}, 'Index']), we will get the string <a href="views">Index</a>.

The idea behind any DSL is to specify a few constructs with a specific structure which is then passed to a function. In this case, the structure that makes up the dsDSL is this array, which has one to three elements; these arrays have a specific structure. If generate thoroughly validates its input (and it is both easy and important to thoroughly validate input, since these validation rules are the precise analog of a DSL’s syntax), it will tell you exactly where you went wrong with your input. After a while, you’ll start to recognize what distinguishes a valid structure in a dsDSL, and this structure will be highly suggestive of the underlying thing it generates.

Now, what are the merits of a dsDSL in contraposition to a DSL?

  • A dsDSL is an integral part of your code. It leads to lower line counts, file counts, and an overall reduction of overhead.
  • dsDSLs are easy to parse (hence easier to implement and modify). Parsing is merely iterating through the elements of an array or object. Likewise, dsDSLs are comparatively easy to design because instead of creating a new syntax (that everybody will hate) you can stick with the syntax of your programming language (which everybody hates but at least they already know it).
  • A dsDSL has all the power of a programming language. This means that a dsDSL, when properly employed, has the advantage of both a high and a low level tool.

Now, the last claim is a strong one, so I’m going to spend the rest of this section supporting it. What do I mean by properly employed? To see this in action, let’s consider an example in which we want to construct a table to display the information from an array named DATA.

var DATA = [
   {id: 1, description: 'Product 1', price: 20,  onSale: true,  categories: ['a']},
   {id: 2, description: 'Product 2', price: 60,  onSale: false, categories: ['b']},
   {id: 3, description: 'Product 3', price: 120, onSale: false, categories: ['a', 'c']},
   {id: 4, description: 'Product 4', price: 45,  onSale: true,  categories: ['a', 'b']}

In a real application, DATA will be generated dynamically from a database query.

Moreover, we have a FILTER variable which, when initialized, will be an array with the categories we want to display.

We want our table to:

  • Display table headers.
  • For each product, show the fields: description, price and categories.
  • Don’t print the id field, but add it as an id attribute for each row. ALTERNATE VERSION: Add an id attribute to each tr element.
  • Place a class onSale if the product is on sale.
  • Sort the products by descending price.
  • Filter certain products by category. If FILTER is an empty array, we will display all products. Otherwise, we will only display the products where the category of the product is contained within FILTER.

We can create the presentation logic that matches this requirement in ~20 lines of code:

function drawTable (DATA, FILTER) {

   var printableFields = ['description', 'price', 'categories'];

   DATA.sort (function (a, b) {return a.price - b.price});

   return ['table', [
      ['tr', (printableFields, function (field) {
         return ['th', field];
      })], (DATA, function (product) {
         var matches = (! FILTER || FILTER.length === 0) || dale.stop (product.categories, true, function (category) {
            return FILTER.indexOf (category) !== -1;

         return matches === false ? [] : ['tr', {
            class: product.onSale ? 'onsale' : undefined
         }, (printableFields, function (field) {
            return ['td', product [field]];

I concede this is not a straightforward example, however, it represents a fairly simple view of the four basic functions of persistent storage, also known as CRUD. Any non-trivial web application will have views that are more complex than this.

Let’s now see what this code is doing. First, it defines a function, drawTable, to contain the presentation logic of drawing the product table. This function receives DATA and FILTER as parameters, so it can be used for different data sets and filters. drawTable fulfills the double role of partial and helper.

   var drawTable = function (DATA, FILTER) {

The inner variable, printableFields, is the only place where you need to specify which fields are printable ones, avoiding repetition and inconsistencies in the face of changing requirements.

   var printableFields = ['description', 'price', 'categories'];

We then sort DATA according to the price of its products. Notice that different and more complex sort criteria would be straightforward to implement since we have the entire programming language at our disposal.

   DATA.sort (function (a, b) {return a.price - b.price});

Here we return an object literal; an array which contains table as its first element and its contents as the second. This is the dsDSL representation of the <table> we want to create.

   return ['table', [

We now create a row with the table headers. To create its contents, we use which is a function like, but one that also works for objects. We will iterate printableFields and generate table headers for each of them:

      ['tr', (printableFields, function (field) {
         return ['th', field];

Notice that we have just implemented iteration, the workhorse of HTML generation, and we didn’t need any DSL constructs; we only needed a function to iterate a data structure and return dsDSLs. A similar native, or user-implemented function, would have done the trick as well.

Now iterate through the products contained in DATA. (DATA, function (product) {

We check whether this product is left out by FILTER. If FILTER is empty, we will print the product. If FILTER is not empty, we will iterate through the categories of the product until we find one that is contained within FILTER. We do this using dale.stop.

         var matches = (! FILTER || FILTER.length === 0) || dale.stop (product.categories, true, function (category) {
            return FILTER.indexOf (category) !== -1;

Notice the intricacy of the conditional; it is precisely tailored to our requirement and we have total freedom for expressing it because we are in a programming language rather than a DSL.

If matches is false, we return an empty array (so we don’t print this product). Otherwise, we return a <tr> with its proper id and class and we iterate through printableFields to, well, print the fields.

         return matches === false ? [] : ['tr', {
            class: product.onSale ? 'onsale' : undefined
         }, (printableFields, function (field) {
            return ['td', product [field]];

Of course we close everything that we opened. Isn’t syntax fun?


Now, how do we incorporate this table into a wider context? We write a function named drawAll that will invoke all functions that generate the views. Apart from drawTable, we might also have drawHeaderdrawFooter and other comparable functions, all of which will return dsDSLs.

var drawAll = function () {
   return generate ([
      drawHeader (),
      drawTable (DATA, FILTER),
      drawFooter ()

If you don’t like how the above code looks, nothing I say will convince you. This is a dsDSL at its best. You might as well stop reading the article (and drop a mean comment too because you’ve earned the right to do so if you’ve made it this far!). But seriously, if the code above doesn’t strike you as elegant, nothing else in this article will.

For those who are still with me, I would like to go back to the main claim of this section, which is that a dsDSL has the advantages of both the high and the low level:

  • The advantage of the low level resides in writing code whenever we want, getting out of the straightjacket of the DSL.
  • The advantage of the high level resides in using literals that represent what we want to declare and letting the functions of the tool convert that into the desired end state (in this case, a string with HTML).

But how is this truly different from purely imperative code? I think ultimately the elegance of the dsDSL approach boils down to the fact that code written in this way mostly consists of expressions, instead of statements. More precisely, code that uses a dsDSL is almost entirely composed of:

  • Literals that map to lower level structures.
  • Function invocations or lambdas within those literal structures that return structures of the same kind.

Code that consists mostly of expressions and which encapsulate most statements within functions is extremely succinct because all patterns of repetition can be easily abstracted. You can write arbitrary code as long as that code returns a literal that conforms to a very specific, non-arbitrary form.

A further characteristic of dsDSLs (which we don’t have time to explore here) is the possibility of using types to increase the richness and succinctness of the literal structures. I will expound on this issue on a future article.

Might it be possible to create dsDSLs beyond Javascript, the One True Language? I think that it is, indeed, possible, as long as the language supports:

  • Literals for: arrays, objects (associative arrays), function invocations, and lambdas.
  • Runtime type detection
  • Polymorphism and dynamic return types

I think this means that dsDSLs are tenable in any modern dynamic language (i.e.: Ruby, Python, Perl, PHP), but probably not in C or Java.

Walk, Then Slide: How To Unfold The High From The Low

In this section I will attempt to show a way for unfolding a high level tool from its domain. In a nutshell, the approach consists of the following steps

  1. Take two to four problems that are representative instances of a problem domain. These problems should be real. Unfolding the high level from the low one is a problem of induction, so you need real data to come up with representative solutions.
  2. Solve the problems with no tool in the most straightforward way possible.
  3. Stand back, take a good look at your solutions, and notice the common patterns among them.
  4. Find the patterns of representation (high level).
  5. Find the patterns of generation (low level).
  6. Solve the same problems with your high level layer and verify that the solutions are indeed correct.
  7. If you feel that you can easily represent all the problems with your patterns of representation, and the generation patterns for each of these instances produce correct implementations, you’re done. Otherwise, go back to the drawing board.
  8. If new problems appear, solve them with the tool and modify it accordingly.
  9. The tool should converge asymptotically to a finished state, no matter how many problems it solves. In other words, the complexity of the tool should remain constant, rather than growing with the amount of problems it solves.

Now, what the hell are patterns of representation and patterns of generation? I’m glad you asked. The patterns of representation are the patterns in which you should be able to express a problem that belongs to the domain that concerns your tool. It is an alphabet of structures that allows you to write any pattern you might wish to express within its domain of applicability. In a DSL, these would be the production rules. Let’s go back to our dsDSL for generating HTML.

The humble HTML tag is a good example of patterns of representation. Let’s take a closer look at these basic patterns.
The humble HTML tag is a good example of patterns of representation. Let’s take a closer look at these basic patterns.

The patterns of representation for HTML are the following:

  • A single tag: ['TAG']
  • A single tag with attributes: ['TAG', {attribute1: value1, attribute2: value2, ...}]
  • A single tag with contents: ['TAG', 'CONTENTS']
  • A single tag with both attributes and contents: ['TAG', {attribute1: value1, ...}, 'CONTENTS']
  • A single tag with another tag inside: ['TAG1', ['TAG2', ...]]
  • A group of tags (standalone or inside another tag): [['TAG1', ...], ['TAG2', ...]]
  • Depending on a condition, place a tag or no tag: condition ? ['TAG', ...] : [] / Depending on a condition, place an attribute or no attribute: ['TAG', {class: condition ? 'someClass': undefined}, ...]

These instances can be represented with the dsDSL notation we determined in the previous section. And this is all you need to represent any HTML you might need. More sophisticated patterns, such as conditional iteration through an object to generate a table, may be implemented with functions that return the patterns of representation above, and these patterns map directly to HTML tags.

If the patterns of representation are the structures you use to express what you want, the patterns of generation are the structures your tool will use to convert patterns of representation into the lower level structures. For HTML, these are the following:

  • Validate the input (this is actually is an universal pattern of generation).
  • Open and close tags (but not the void tags, like <input>, which are self-closing).
  • Place attributes and contents, escaping special characters (but not the contents of the <style> and <script> tags).

Believe it or not, these are the patterns you need to create an unfolding dsDSL layer that generates HTML. Similar patterns can be found for generating CSS. In fact, lith does both, in ~250 lines of code.

One last question remains to be answered: What do I mean by walk, then slide? When we deal with a problem domain, we want to use a tool that delivers us from the nasty details of that domain. In other words, we want to sweep the low level under the rug, the faster the better. The walk, then slide approach proposes exactly the opposite: spend some time on the low level. Embrace its quirks, and understand which are essential and which can be avoided in the face of a set of real, varied, and useful problems.

After walking in the low level for some time and solving useful problems, you will have a sufficiently deep understanding of their domain. The patterns of representation and generation will then arise naturally; they are wholly derived from the nature of the problem they intend to solve. You can then write code that employs them. If they work, you will be able to slide through problems where you recently had to walk through them. Sliding means many things; it implies speed, precision and lack of friction. Maybe more importantly, this quality can be felt; when solving problems with this tool, do you feel like you’re walking through the problem, or do you feel that you’re sliding through it?

Maybe the most important thing about an unfolded tool is not the fact that it frees us from having to deal with the low level. Rather, by capturing the empiric patterns of repetition in the low level, a good high level tool allows us to understand fully the domain of applicability.

An unfolded tool will not just solve a problem – it will enlighten you about the problem’s structure.

So, don’t run away from a worthy problem. First walk around it, then slide through it.

What’s a Bitcoin full node?

The Bitcoin network is a collection of computers all over the world running the Bitcoin Core software that verifies transactions and blocks. It’s the distribution of these “nodes” (the term for a computer attached to the network) and the fact that anyone can set one up that makes Bitcoin “decentralized.” This means that anyone anywhere can set up a Bitcoin node as long as they have access to a computer with the required power and an internet connection. And if even one node is up and running, Bitcoin lives on.

Global Bitcoin Nodes Distribution

Most Bitcoin nodes also act as a Bitcoin client, which allows transactions to be sent to the network. This means a node acts as your personal interface with the Bitcoin network as a whole. Running a node ensures that your Bitcoin transactions are verified and sent to whoever you’re transacting with. This puts the power to send uncensorable money across the world or across the street in your hands and contributes to the security and strength of the Bitcoin network itself.

Running a node is different than mining Bitcoin, which involves running special software that works to solve or complete new blocks on the network, releasing a certain number of Bitcoin to those computers responsible for adding a block to the blockchain. While mining Bitcoin has become quite resource-intensive and much of the mining work is being done by large companies with data centers devoted to the process, running  full nodes is accessible to anyone.

OK, I get it…. Why should I run a full node?

There are various reasons to set up a full node yourself:

    1. You believe in Bitcoin and want the network to grow and succeed. Every node added to the network brings us closer to a future where everyone is transacting on the Bitcoin network and no governments or other third parties can do anything to stop it.
    2. You intend to use the Bitcoin network to transact a lot and want to ensure that your transactions are verified. The idea behind Bitcoin is the removal of trust from the monetary system: you don’t have to trust a bank to hold or send your money. But as long as you’re not running your own node, you’re still trusting someone who IS running nodes to verify that transaction in a timely manner. Taking your financial life into your own hands is empowering.
    3. You can tell all your friends that you don’t just own Bitcoin, you ARE Bitcoin… at least part of it 🙂

I’m convinced! How can I set up a full node?

There are 3 methods to go about setting up your own Bitcoin node as of right now, ranging from pretty technical and time-intensive to really easy but a little more expensive. As development and adoption of Bitcoin technology continue, this process will only get easier and cheaper. If you want to get ahead of the game and jump into the action now though, you’ll do it in one of these ways:

  • Setting up a node on your own computer (or Raspberry Pi or any machine with the required hardware), or
  • Setting up a node in the cloud using hosting service like Amazon Web Services, Digital Ocean or any number of other providers, or
  • Buying a standalone “node-in-a-box” device that sets up the node automatically (Skip to the bottom to hear about this option)

I’m ready to node, let’s get to it!

While the first two methods are very similar in process, there are considerations for each.

1. Choose your machine!

You will need to set the node up on a computer that has these minimum required hardware specifications:

  • A recent version of macOS, Linux, or Windows operating system
  • 145GB of free disk space
  • 2GB of RAM
  • A high-speed internet connection (at least 50kB/s)
  • Unlimited or very high upload/download limits (a node can upload ~200GB and download ~20GB per month)

If you choose to make use of the cloud and set up on a virtual server, make sure that whatever machine you rent has the same specifications! The cheapest option I found was from Scaleway, where you can get a machine powerful enough to run a node for around $8/month. To do this you’ll:

  • head to
  • sign up for a C1 instance (their lowest option)
  • add on 3 50GB storage volumes to make sure you have enough storage for the whole Bitcoin blockchain.

There are plenty of other providers out there that can handle the node, so go ahead and do some shopping or use your favorite if you have one. Digital Ocean and Amazon Web Services are popular options but will cost you a bit more.

Note: Pay attention to the bandwidth or data limits on any cloud solution, as many providers out there will rate limit your connection after a certain point.

2. Start the setup!

If you’re planning to run your node on a computer locally, you can decide whether you’d like to run the Bitcoin Core software as a standard application (the GUI or Graphical User Interface) or through the command line as a background process. If you’re working on the cloud you’re most likely going to use the command line method.

I wanna run the GUI software!

So you like graphical interfaces. Great! Here’s the process:

  • Download the latest Bitcoin Core GUI from the download page for your operating system of choice.
  • Run the software and you will be prompted to choose a directory for storing the blockchain data. Unless you have a specific preference here, go ahead and leave the “Use the default data directory” option checked and hit OK.
  • At this point on Windows computers, you may have a firewall prompt appear asking for permission to let Bitcoin communicate over the web. Check all boxes and allow these permissions.
  • The software should begin downloading the blockchain. This will take anywhere from 12 hours to a couple of days depending on your internet speeds and bandwidth. Let it finish and you’re officially running a Bitcoin full node! See the Network Configuration section below to make sure your node has the access it needs to run properly.

I wanna use the command line!

So you dig the command line, or you’d rather have Bitcoin Core run in the background? Sweet! Here we go:

  • To simplify this process, (formerly has put together a simple-to-use script that makes it a breeze to install a node via the command line!
  • Open up the Command Prompt (Windows) or the Terminal (macOS and Linux) and paste this command:
    curl | sh
  • Hit enter and you should see a welcome message pop up (like this one):
Bitnodes Install Full Nodes
  • Let the process run its course! It will download the Bitcoin Core software and attempt to set up port forwarding. If it can’t set up port forwarding automatically you’ll see a message appear like this one:
Bitcoin Core Error Message
  • You should also receive a success message! Your node is installed and running. Head down the Network Configuration section below to make sure everything is setup correctly for proper functioning.

3. Network Configuration

Whether you’ve set up a node using the standard GUI software or through the command line, there will be some network setup required to make sure the nodes can send and receive connections from the Bitcoin network.

There are two jobs to complete here:

  1. Giving your computer a Static IP Address
  2. Setting up Port Forwarding

Instead of walking through this whole process, I’ll let the wonderful folks over at take care of it! See the official guide for step-by-step instructions on accessing your router and setting it up to handle the node correctly.

If you’ve set up your node in the cloud, this process can be very different based on the service provider. Reach out to the support team for your specific provider or head over to SuperUser (a question and answer site for this sort of thing) to get help!

So… what about the Node-in-a-Box?

This is by far the easiest way to set up a full node right now. A simple plug-and-play box that you’d plug into your internet router just like a cable box. This lets you run a dedicated node without installing anything on your computer or another machine. You WILL still need to complete the network configuration steps outlined in the section above though!

The only project seemingly available right now is Bitseed. The Bitseed is currently pretty pricey at around $360, but from reviews, it seems to work as advertised and keeps things very simple. There are bound to be competitors coming out of the woodwork in no time, so keep an eye out as the space matures.


Once the software is running, the blockchain has completely synced, and your network settings are correct, you’ve done it! You’re officially a contributing member of the Bitcoin network. Welcome to the future of money.

More Nodes is Stronger Bitcoin

Wrapping Up

Bitcoin is powered by nodes.

More nodes = stronger Bitcoin.

You should run a node. Maybe two.

This article was previously published on

About the Author:

James Risberg

I’m a casual nerd who likes crypto and community building. Software dev, social psychologist and sipper of tea. I love art of all kinds, actively seeking truth, and alliteration.


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