All articles tagged #asyncio

Python is booming and Flask is a pretty popular web-framework nowadays. Probably, quite some new projects are being started in Flask. But people should be aware, it's synchronous by design and ASGI is not a thing yet. So, if someday you realize that your project really needs asynchronous I/O but you already have a considerable codebase on top of Flask, this tutorial is for you. The charming gevent library will enable you to keep using Flask while start benefiting from all the I/O being asynchronous. In the tutorial we will see:

How to monkey patch a Flask app to make it asynchronous w/o changing its code.
How to run the patched application using gevent.pywsgi application server.
How to run the patched application using Gunicorn application server.
How to run the patched application using uWSGI application server.
How to configure Nginx proxy in front of the application server.
[Bonus] How to use psycopg2 with psycogreen to make PostgreSQL access non-blocking.

Explaining async/await in 200 lines of code

May 2, 2019 (Updated: August 1, 2021)

Programming

In the previous article, we learned how to implement a simple but workable event loop. However, programs which are supposed to be run by the event loop are full of callbacks. This is the usual problem of event-loop-driven environments. When business logic becomes reasonably complicated, callbacks make program's code hardly readable and painfully maintainable. And the callback hell begins! There is plenty of ways to deal with the artificial complexity arose due to callbacks, but the most impressive one is to make the code ~~great~~ flat again. And by flat, I mean callback-less and synchronous-like. Usually, it's done by introducing async/await syntactic feature. But every high-level abstraction is built on top of some basic and fundamental ideas. Let's check the async/await sugar out and see what exactly happens under the hood.

Callbacks vs. async/await (code excerpt).

Explaining event loop in 100 lines of code

April 25, 2019 (Updated: August 1, 2021)

Programming

There is plenty of articles out there about the event loop. However, as a software engineer, I prefer to read code, not text. And there is no better way of learning a new concept than implementing it yourself. So, let's try to grasp the idea of the event loop by coding a new ~~and shiny~~ one.

In the article, I'll try to describe the idea of the event loop in general, not a specific implementation of the event loop in Node.js or Python, or some other language/library.

Save the day with gevent

April 17, 2019 (Updated: October 9, 2021)

Programming

One day you were hired by a startup to build yet another web ~~site~~ service. The problem sounded similar to numerous back-ends you had been doing before. So, you decided to move with python to be conservative enough and pick flask to be lightweight but yet powerful enough. Nobody was fired for ~~buying IBM~~ starting things in python, wise man's choice.

Magister Yoda: Why am I called wise? I can barely speak English!

Node.js Writable streams distilled

April 7, 2019 (Updated: January 3, 2021)

Programming

Writable streams are an abstraction for a destination to which data is written... And this time it's a concise abstraction! Compared to vague readable streams (multiple operation modes behind single abstraction) writable streams implement only one mode and hence expose only one essential method write(chunk). Nevertheless, the idea of writable streams is not trivial and it's due to one nice feature it provides - backpressure. Let's try to wrap our mind around writable stream abstraction.