Lightweight in-process concurrent programming
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The greenlet package is a spin-off of Stackless, a version of CPython that supports micro-threads called "tasklets". Tasklets run pseudo-concurrently (typically in a single or a few OS-level threads) and are synchronized with data exchanges on "channels".

A "greenlet", on the other hand, is a still more primitive notion of micro-thread with no implicit scheduling; coroutines, in other words. This is useful when you want to control exactly when your code runs. You can build custom scheduled micro-threads on top of greenlet; however, it seems that greenlets are useful on their own as a way to make advanced control flow structures. For example, we can recreate generators; the difference with Python's own generators is that our generators can call nested functions and the nested functions can yield values too. Additionally, you don't need a "yield" keyword. See the example in tests/

Greenlets are provided as a C extension module for the regular unmodified interpreter.

Greenlets are lightweight coroutines for in-process concurrent programming.

Who is using Greenlet?

There are several libraries that use Greenlet as a more flexible alternative to Python's built in coroutine support:

Getting Greenlet

The easiest way to get Greenlet is to install it with pip or easy_install:

pip install greenlet
easy_install greenlet

Source code archives and windows installers are available on the python package index at

The source code repository is hosted on github:

Documentation is available on