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


  • 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 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, 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!


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 = [

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

pool = eventlet.GreenPool()

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


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