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How to inspect and clear Python’s functools.lru_cache

Python’s functools.lru_cache binds two additional functions to decorated functions:

Flakey tests

I’ve found functools.lru_cache use to be a common factor of flakey tests, where behaviour changes depending on the order in which tests run (which affects which value gets cached). The symptoms are often that a test passes when run on its own but intermittently fails when run as part of a larger group.

Avoid this by clearing related LRU caches as part of each test’s tear-down process:

import pytest
from somemodule import cached_function

def clear_lru_cache():
    # Execute the test...

    # ...then clear the LRU cache.