greenlet

3.3.2 · active · verified Sat Mar 28

greenlet is a Python package that provides lightweight in-process concurrent programming through micro-threads called 'greenlets'. The current version is 3.3.2, released on February 20, 2026. The library has a stable release cadence, with updates addressing compatibility and performance improvements.

Warnings

breaking Support for Python 3.9 was dropped in version 3.3.0.
Fix: Upgrade your Python environment to version 3.10 or later.
breaking Support for Python 3.7 and 3.8 was removed in version 3.2.0.
Fix: Upgrade your Python environment to version 3.9 or later.
gotcha Mixing greenlets and signal handlers can lead to hangs if the signal handler switches greenlets without returning.
Fix: Ensure that signal handlers return control to the main greenlet without switching.
gotcha Using non-reentrant native functions within greenlets can cause subtle issues.
Fix: Avoid calling non-reentrant native functions from multiple greenlets.
gotcha Greenlets cannot switch between different Python threads.
Fix: Ensure that greenlet switching occurs within the same thread.
gotcha Garbage collection of greenlets can lead to 'GreenletExit' exceptions if not handled properly.
Fix: Implement appropriate exception handling to manage 'GreenletExit' during garbage collection.

Install

pip install greenlet Install greenlet

Imports

greenlet
```
from greenlet import greenlet
```
Directly importing 'greenlet' does not provide access to the 'greenlet' class; use 'from greenlet import greenlet' instead.
getcurrent
```
from greenlet import getcurrent
```
To access the 'getcurrent' function, use 'from greenlet import getcurrent'.

Quickstart

This example demonstrates creating and switching between two greenlets. 'gr1' starts 'test1', which switches to 'gr2' running 'test2', and then switches back to 'gr1'.

from greenlet import greenlet

def test1():
    print("[gr1] main  -> test1")
    gr2.switch()
    print("[gr1] test1 <- test2")
    return 'test1 done'

def test2():
    print("[gr2] test1 -> test2")
    gr1.switch()

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

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