Pykka

4.4.2 verified Fri May 01 auth: no python

Pykka is a Python implementation of the actor model, providing concurrency primitives for building distributed and concurrent systems. Version 4.4.2 runs on Python >=3.10. New releases are sporadic.

pip install pykka

Common errors

error ModuleNotFoundError: No module named 'pykka' ↓

cause Pykka not installed or wrong Python environment.

fix

Install with 'pip install pykka' and verify Python version >=3.10.

error AttributeError: 'MyActor' object has no attribute 'start' ↓

cause Attempting to call start() on an instance instead of the class.

fix

Use MyActor.start() (class method) not my_actor.start().

error TimeoutError: Actor call timed out after ... seconds ↓

cause Actor's on_receive never returned a value (or deadlocked).

fix

Ensure every on_receive returns a result. If no result, call actor.stop() and return a default.

Warnings

gotcha Actors are not threadsafe; avoid sharing mutable state between actors. Use message passing only. ↓

fix Design actors as isolated units communicating via messages (dicts or immutable objects).

gotcha Unlike the standard library, Pykka actors must be stopped explicitly to release resources. ActorRegistry will not clean them up automatically. ↓

fix Call actor.stop() or use a context manager: with Greeter.start() as actor: ...

breaking In Pykka 4.x, on_receive must return a value or raise an exception; previously None was allowed and would cause hangs. ↓

fix Ensure on_receive always returns a value (or call actor.stop() explicitly without a return).

gotcha Proxy() and get() are blocking. Using them inside an actor's on_receive can cause deadlocks. ↓

fix Use future.get() only outside actors, or use call() with a callback instead.

Imports

Actor
```
from pykka import Actor
```
Standard import
ThreadingActor
```
from pykka import ThreadingActor
```
Preferred for I/O-bound tasks
ActorRef
```
from pykka import ActorRef
```
Reference to an actor instance
ActorRegistry
```
from pykka import ActorRegistry
```
Global registry of actors

getattr

wrong

from pykka.actor import getattr

correct

from pykka import getattr

getattr moved to top-level since v3

Quickstart

Define an actor class, start it, send a message, and stop.

import pykka

class Greeter(pykka.ThreadingActor):
    def __init__(self, greeting='Hi'):
        super().__init__()
        self.greeting = greeting

    def on_receive(self, message):
        return f'{self.greeting}, {message}'

actor = Greeter.start(greeting='Hello').proxy()
print(actor.on_receive('World').get())  # Hello, World
actor.stop()