Eventlet

Eventlet is a concurrent networking library for Python that allows you to change how you run your code, not how you write it.

It uses epoll or kqueue or libevent for highly scalable non-blocking I/O.
Coroutines ensure that the developer uses a blocking style of programming that is similar to threading, but provide the benefits of non-blocking I/O.
The event dispatch is implicit, which means you can easily use Eventlet from the Python interpreter, or as a small part of a larger application.

It's easy to get started using Eventlet, and easy to convert existing applications to use it. Start off by looking at examples, common design patterns, and the list of the basic API primitives.

License: MIT

Currently CPython 2.7 and 3.4+ are supported, but 2.7 and 3.4 support is deprecated and will be removed in the future, only CPython 3.5+ support will remain.

API Documentation

Installation

To install latest PyPI release:
```
pip install eventlet
```
Manually lock version in requirements, if your build/development process doesn't automate it:
```
# requirements.txt
eventlet==x.y
```
Eventlet team is commited to have only stable code in master branch, so recommended way to install is from latest master commit:
```
pip install https://github.com/eventlet/eventlet/archive/master.zip
```
Beware, http…zip link in requirements.txt will repeat download and installation even if you specify link to particular commit.
Earlier versions available at Eventlet on PyPI

Development

Development, issue tracking happens at Eventlet on Github

We had Mercurial repository on Bitbucket, but it's not used anymore.

Pull request policy

Test is required
One commit is strongly preferred, except for very big changes
Commit message should follow the following formula:
```
subsystem: description of why the change is useful

optional details

links to related issues or websites
```
The why part is very important. Diff already says what you have done. But nobody knows why.
Feel free to append yourself into AUTHORS file, sections Thanks To or Contributors.

If you don't like these rules, raw patches are more than welcome!

Bugs

Please be sure to report bugs as effectively as possible, to ensure that we understand and act on them quickly.

Usually open issue at Github

In special cases, to contact current maintainers directly, look up info on Github project page.

Web Crawler Example¶

This is a simple web “crawler” that fetches a bunch of urls using a coroutine pool. It has as much concurrency (i.e. pages being fetched simultaneously) as coroutines in the pool.

import eventlet
# note: this urllib import doesn't work in Python2
from eventlet.green.urllib.request import urlopen


urls = [
    "http://www.google.com/intl/en_ALL/images/logo.gif",
    "https://wiki.secondlife.com/w/images/secondlife.jpg",
    "http://us.i1.yimg.com/us.yimg.com/i/ww/beta/y3.gif",
]


def fetch(url):
    return urlopen(url).read()


pool = eventlet.GreenPool()

for body in pool.imap(fetch, urls):
    print("got body", len(body))