PyBevy is in an early and experimental stage. The API is incomplete, subject to breaking changes without notice, and you should expect bugs. Many features are still under development.
System Closure
Use closures and captured variables as systems.
Introduction
In PyBevy, any callable with the right parameter signature can be a system. This includes closures that capture variables from their enclosing scope — useful for parameterized or stateful systems.
from pybevy.prelude import *Simple Function System
The most basic form — a plain function:
def simple_system() -> None:
print("I am a simple system!")Stateful Closure
A closure that captures a counter variable. Each call increments the counter.
call_count = [0]
def counting_system() -> None:
call_count[0] += 1
if call_count[0] % 60 == 0:
print(f"Counting system called {call_count[0]} times")Running the App
@entrypoint
def main(app: App) -> App:
return (
app
.add_plugins(DefaultPlugins)
.add_systems(Startup, simple_system)
.add_systems(Update, counting_system)
)
if __name__ == "__main__":
main().run()Running this example
Use PyBevy's hot reload feature to run and develop this example. If you don't have PyBevy installed, check out the Quick Start guide.
The code will reload automatically when you make changes to the file.
From Python to Rust
Notice how the core concepts in the code—Commands, Assets, App, and Systems—are identical to the original Bevy example?
This is the power of pybevy! It lets you learn Bevy's powerful, data-driven architecture in friendly Python.
When your project grows and you're ready for maximum, native performance, you'll already know the concepts to start writing systems in Bevy Engine with Rust.