looptime

0.7 verified Mon Apr 27 auth: no python

Utility to fast-forward asyncio event loop time for deterministic testing. Current version 0.7, requires Python >=3.10. Released as a standalone package to replace pytest-asyncio's `loop_context` for controlling virtual time.

pip install looptime

Common errors

error AttributeError: module 'looptime' has no attribute 'Looper' ↓

cause Incorrect import: from looptime import looptime or misspelled class name.

fix

Use 'from looptime import Looper' (capital L).

error RuntimeError: Cannot change event loop time outside of looptime context ↓

cause Calling advance() or other time manipulation methods without first entering a Looper context.

fix

Wrap the code in 'async with Looper():' before calling advance().

Warnings

gotcha Looper must be used as a context manager (async with). Simply creating a Looper instance without entering will not affect event loop timing. ↓

fix Use 'async with Looper() as looper:' to ensure the looper is properly activated.

gotcha Advancing time via looper.advance() does not automatically wake up tasks; it only moves the clock. Tasks waiting on asyncio.sleep() will only resume when the looper's event loop cycle runs (e.g., after the advance call returns). ↓

fix After calling advance(), await asyncio.sleep(0) to yield control and allow scheduled tasks to run.

Imports

Looper
```
from looptime import Looper
```

Quickstart

Basic usage: create a Looper, enter it as a context manager, advance time, and exit.

import asyncio
from looptime import Looper

async def test_sleep():
    looper = Looper()
    asyncio.get_event_loop().run_until_complete(looper.__aenter__())
    await asyncio.sleep(3600)
    # Without looper, this would block for an hour.
    looper.advance(3600)
    # Now the sleep completes immediately.
    await looper.__aexit__(None, None, None)