greenlet

Lightweight in-process concurrent programming

greenlet Permissive license MIT AND PSF-2.0 Active ★ 1,837 v3.5.5 released 2026-08-10

Install

greenlet on PyPI

pip

pip install greenlet

uv

uv add greenlet

poetry

poetry add greenlet

Package facts

License	MIT AND PSF-2.0 (permissive)
Python support	supports the current Python release (>=3.10)
Install friction	medium — platform-specific wheel
Runtime dependencies	none
Maintenance	actively maintained — 3 days since the last release
Last repo commit	2026-08-10
First released	2006-01-10
Popularity	one of the 100 most-downloaded packages on PyPI (30-day window, as of 2026-08-13)
Known vulnerabilities	none known (OSV.dev, checked 2026-08-13)

Evidence: greenlet-3.5.5-cp310-cp310-macosx_11_0_universal2.whl; greenlet-3.5.5-cp310-cp310-manylinux_2_24_aarch64.manylinux_2_28_aarch64.whl; greenlet-3.5.5-cp310-cp310-manylinux_2_24_ppc64le.manylinux_2_28_ppc64le.whl; greenlet-3.5.5-cp310-cp310-manylinux_2_24_s390x.manylinux_2_28_s390x.whl; greenlet-3.5.5-cp310-cp310-manylinux_2_24_x86_64.manylinux_2_28_x86_64.whl; greenlet-3.5.5-cp310-cp310-manylinux_2_39_riscv64.whl; greenlet-3.5.5-cp310-cp310-musllinux_1_2_aarch64.whl; greenlet-3.5.5-cp310-cp310-musllinux_1_2_x86_64.whl; greenlet-3.5.5-cp310-cp310-win_amd64.whl; greenlet-3.5.5-cp311-cp311-macosx_11_0_universal2.whl; greenlet-3.5.5-cp311-cp311-manylinux_2_24_aarch64.manylinux_2_28_aarch64.whl; greenlet-3.5.5-cp311-cp311-manylinux_2_24_ppc64le.manylinux_2_28_ppc64le.whl; greenlet-3.5.5-cp311-cp311-manylinux_2_24_s390x.manylinux_2_28_s390x.whl; greenlet-3.5.5-cp311-cp311-manylinux_2_24_x86_64.manylinux_2_28_x86_64.whl; greenlet-3.5.5-cp311-cp311-manylinux_2_39_riscv64.whl; greenlet-3.5.5-cp311-cp311-musllinux_1_2_aarch64.whl; greenlet-3.5.5-cp311-cp311-musllinux_1_2_x86_64.whl; greenlet-3.5.5-cp311-cp311-win_amd64.whl; greenlet-3.5.5-cp311-cp311-win_arm64.whl; greenlet-3.5.5-cp312-cp312-macosx_11_0_universal2.whl

Keywords: greenlet, coroutine, concurrency, threads, cooperative

Development Status :: 5 - Production/StableIntended Audience :: DevelopersNatural Language :: EnglishOperating System :: OS IndependentProgramming Language :: CProgramming Language :: PythonProgramming Language :: Python :: 3Programming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14Programming Language :: Python :: 3.15Topic :: Software Development :: Libraries :: Python Modules

About greenlet

from the package's own PyPI description — quoted content, verbatim

.. This file is included into docs/history.rst

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...

Read as markdown · JSON record · Source repository · Homepage · Docs

AI interpretation — verify before relying

AI-generated interpretation of the package facts above; every digit, version, license, or vulnerability id it cites is grounded in the facts already shown on this page

Greenlet provides lightweight coroutines for in-process concurrent programming, enabling you to build custom micro-threads with explicit control flow without relying on the operating system's threading.

Medium install friction due to compiled C extension wheels across many platforms (Python 3.10–3.15, macOS, Linux variants, Windows). Maintenance is active with a recent release (3 days old) and ongoing repository activity, reducing long-term risk.

Dual-licensed under MIT and PSF-2.0, both permissive licenses. You may use, modify, and distribute greenlet freely in commercial and private projects with minimal restrictions.

Usage

pip install greenlet

from greenlet import greenlet

def test1():
    print("test1 1")
    gr2.switch()
    print("test1 2")

def test2():
    print("test2 1")
    gr1.switch()
    print("test2 2")

gr1 = greenlet(test1)
gr2 = greenlet(test2)
gr1.switch()

Requires Python >=3.10. C compiler needed to build from source on platforms without pre-built wheels.

Verdict: Greenlet is a stable, actively maintained library (top 100 PyPI, no known vulnerabilities) offering a proven foundation for building concurrent systems with explicit control flow. The permissive dual MIT/PSF-2.0 license poses no legal friction. Medium install friction from C extension compilation is typical and manageable for most environments.

Needs verification

Whether pre-built wheels cover your specific platform/architecture combination (though coverage is extensive).
Performance characteristics and memory overhead compared to asyncio or threading for your specific workload.

lightweight coroutines pythonconcurrent programming microthreadsgreenlet cooperative multitaskingin-process concurrency controlpython coroutine librarytasklet alternative to threadsexplicit scheduling concurrency