pypubsub

library4.0.7pypypi✓ verified 87d ago

PyPubSub is a lightweight, thread-safe publish-subscribe messaging library for Python. It provides a simple API to enable decoupled communication between different parts of an application. The current version is 4.0.7, focusing on Python 3 compatibility and performance. Releases typically happen as needed to address bug fixes, new Python version compatibility, or major feature/protocol changes.

communication workflow

pip install pypubsub

github ↗package ↗docs ↗

INSTALL

IMPORT

SIG · PYPUBSUB

pypubsub

communicationpythonv4.0.7

Install

1.5s avg

Import

51ms

Disk

16MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v4.0.7 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.920 runs

installs and imports cleanly · install 0.0s · import 0.054s · 18.3MB

glibc

py 3.10–3.920 runs

installs and imports cleanly · install 1.5s · import 0.048s · 19MB

16MB installed

● package 16MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

pub

✓ from pubsub import pub

✗ from pypubsub import pub

The main messaging object 'pub' is imported from the 'pubsub' module within the 'pypubsub' package.

This quickstart demonstrates how to subscribe functions to a topic and publish messages. Listeners can accept positional and keyword arguments, matching the arguments passed to `sendMessage`. The `pub` object manages all subscriptions and publications.

from pubsub import pub def listener_a(arg1, arg2='default'): print(f"Listener A received: {arg1=}, {arg2=}") def listener_b(arg1, **kwargs): print(f"Listener B received: {arg1=}, kwargs: {kwargs}") # Subscribe listeners to a topic pub.subscribe(listener_a, 'my_topic') pub.subscribe(listener_b, 'my_topic') # Publish a message to the topic pub.sendMessage('my_topic', arg1='hello', arg2='world') pub.sendMessage('my_topic', arg1='another_message', extra_key=123) # Unsubscribe a listener pub.unsubscribe(listener_a, 'my_topic') pub.sendMessage('my_topic', arg1='after_unsubscribe')

Debug

Known issues

breakingPyPubSub v4.0.0 and later drops support for Python 2.x. Users on Python 2.7 must use PyPubSub v3.x or migrate to Python 3.

fix

Upgrade your Python environment to 3.7+ and then upgrade PyPubSub to v4.x. If Python 2.7 is strictly required, use `pypubsub==3.4.2`.

affects: <4.0.0

breakingThe 'arg1' messaging protocol, which required calling `pub.setupArg1()`, was abandoned in v4.0.0. Listeners must now accept named arguments directly matching those passed to `sendMessage`, or use `**kwargs`.

fix

Remove any calls to `pub.setupArg1()`. Update listener function signatures to accept named arguments corresponding to the published message's keywords, or use `**kwargs` for flexibility.

affects: <4.0.0

gotchaSpecific older releases (e.g., v3.3.0, v4.0.0, v4.0.3) had known issues when installing from GitHub source distributions directly. Always prioritize installing from PyPI.

fix

Always install PyPubSub using `pip install pypubsub` to ensure you get the correctly packaged version from PyPI. Avoid direct installation from GitHub `.zip` or `.tar.gz` archives unless specifically instructed or for development.

affects: 3.3.0, 4.0.0, 4.0.3

gotchaVersion 3.4.2 was specifically released for Python 2.7. There's an explicit warning not to use it for Python 3+. Installing this version on Python 3 will lead to compatibility issues.

fix

For Python 3 environments, ensure you install PyPubSub v4.0.0 or later. Use `pip install 'pypubsub>=4.0.0'` or simply `pip install pypubsub` to get the latest compatible version.

affects: 3.4.2

Errors

Common errors & fixes

ImportError: No module named 'pubsub'

The PyPubSub library might not be installed, or the import statement is incorrect. The module containing the 'pub' object is named 'pubsub', not 'pypubsub'.

fix

First, ensure the library is installed with `pip install pypubsub`. Then, correct your import statement to `from pubsub import pub`.

AttributeError: module 'pubsub.pub' has no attribute 'setupArg1'

This error occurs in PyPubSub v4.x when attempting to use the `setupArg1` function, which was part of the deprecated 'arg1' messaging protocol in v3.x and earlier.

fix

Remove the call to `pub.setupArg1()`. Update your listener functions to accept named arguments directly, or use `**kwargs` if you need to capture all published arguments without specific naming.

TypeError: listener() got an unexpected keyword argument 'extra_key'

A listener function is called with keyword arguments it does not explicitly define, and it does not have a `**kwargs` parameter to catch arbitrary arguments. This is common if migrating from `arg1` protocol or misconfiguring listener signatures.

fix

Modify your listener function signature to include `**kwargs` if it should accept arbitrary arguments, or ensure all arguments passed via `pub.sendMessage()` are explicitly defined in the listener function signature. For example: `def listener(arg1, arg2, extra_key=None):` or `def listener(arg1, arg2, **kwargs):`

Upgrade

Version history

4.0.7latest on PyPI · released Dec 8, 2025

Audit

Dependencies

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Agent activity

34 hits · last 30 days

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OpenAI (training)

Resources

githubhttps://github.com/schollii/pypubsub ↗

packagehttps://pypi.org/project/pypubsub/ ↗

docshttp://pypubsub.readthedocs.io ↗