Python, do you even async?

Tonight I had the opportunity of speaking at the DomCode meetup in Utrecht. I gave a presentation titled “Python, do you even async?” where I gave an overview on the different ways to do asynchronous I/O in Python, focusing on asyncio for the most part. Here are the slides for those interested:


I had a blast, the venue was great and I got to talk to some great people, I hope to be back!

Thanks a lot to the organizers and App Annie for hosting us and providing the pizza and drinks!


Evergreen 0.2.0 released!

I’m very happy to announce I just released evergreen 0.2.0! From the API standpoint, not many things changed, but a number of important internal changes happened, including a change in how callbacks are scheduled in the event loop, which fixed a nasty issue in¬†Windows.

For those who may not know:

Evergreen is a cooperative multitasking and i/o library for Python. It provides equivalent primitives to those for thread programming, but uses a cooperative model instead.

Operations are driven by an event loop which will run the given tasks and i/o operations in a non-blocking manner while presenting the user a synchronous, blocking API.

Here is the full changelog:

¬†– Revert “Don’t allow futures to be used more than once”
 РBreak potential cycle because we are storing the traceback
 РFixed passing traceback when propagating exception to MAIN parent
 РProcess all callbacks using an Idle handle
 РReplaced use of Future in io module for Result
¬†– Don’t wait for send operation to complete in UDPEndpoint
 РAlways run tests from the right directory
 РFix UDP test case on Windows
 РAdded flush() method to UDPEndpoint and Stream objects
 РCache sockname and peername properties
The code can be downloaded from GitHub, as usual. Hope you like it!

Evergreen: cooperative multitasking and i/o for Python

I’ve been working on-and-off on this project for almost a year during my free time, and after meditating about it I thought: “fuck it, ship it”. Allow me to introduce Evergreen: cooperative multitasking and i/o for Python.

“So, another framework?” I hear you say. Yes, it’s another async framework. But it’s my async framework. I’ve used a number of frameworks for¬†developing¬†servers in Python such as Twisted, Tornado, Eventlet, Gevent and lately Tulip and all of them have great and not so great things, so I decided to blend the ideas I gathered from all of them, add some opinionated¬†decisions, some Stackless flavour and Evergreen was the result.


Evergreeen is a framework which allows developers to write synchronous looking code which is executed asynchronously in a cooperative manner. Evergreen presents an API which looks like the one you would use to write concurrent programs using threads or futures from the Python standard library. The facilities provided by Evergreen are however cooperative, that is, while a task is busy waiting for some i/o other tasks will have their chance to run.

“Show me the code!” I hear you say. Sure, it’s up here on GitHub, released under the MIT license. Since the usual example is a web crawler, here you have one.

Did I mention it supports Python 2 and 3?

“Is it production ready?” I hear you say. It’s still on a very early stage, but I believe the foundation is solid. However, the APIs provided by Evergreen may change a bit until I feel confortable with them. All feedback is welcome, so if you give it a try do let me know!

I’d like to thank all authors of similar libraries for releasing their work as Open Source which I could look into and learn from.

I hope Evergreen can help you solve some problems and you enjoy using it as much as I do developing it.