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Greenlets are lightweight coroutines for in-process concurrent programming.

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 test_generator.py <https://github.com/python-greenlet/greenlet/blob/adca19bf1f287b3395896a8f41f3f4fd1797fdc7/src/greenlet/tests/test_generator.py#L1>_).

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

.. _Stackless: http://www.stackless.com

Who is using Greenlet?

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

Concurrence_
Eventlet_
Gevent_

.. _Concurrence: http://opensource.hyves.org/concurrence/ .. _Eventlet: http://eventlet.net/ .. _Gevent: http://www.gevent.org/

Getting Greenlet

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

pip install greenlet

Source code archives and binary distributions are vailable on the python package index at https://pypi.org/project/greenlet

The source code repository is hosted on github: https://github.com/python-greenlet/greenlet

Documentation is available on readthedocs.org: https://greenlet.readthedocs.io