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Python implementation of functools.lru_cache does not check that argument is callable #144030
Description
Bug report
Bug description:
The C implementation of functools.lru_cache checks whether its argument is callable and raises an exception if not. The Python version does not do that:
import sys
sys.modules['_functools'] = None
import functools
functools.lru_cache()(1) # does not raisewithout blocking the import of _functools you get:
Traceback (most recent call last):
File "/home/cfbolz/projects/cpython/functoolserror.py", line 5, in <module>
functools.lru_cache()(1)
~~~~~~~~~~~~~~~~~~~~~^^^
File "/home/cfbolz/projects/cpython/Lib/functools.py", line 598, in decorating_function
wrapper = _lru_cache_wrapper(user_function, maxsize, typed, _CacheInfo)
TypeError: the first argument must be callableI think this should simply be fixed in the Python implementation and will prepare a patch.
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
Activity
cfbolz commentedon Jan 19, 2026
(bug found by @zahinwahab via fuzzing and reported first here: pypy/pypy#5369 )
gh-144030: Add check that argument is callable to Python version of f…
vstinner commentedon Jan 21, 2026
Merged, thanks for the fix @cfbolz.
pythongh-144030: Add check that argument is callable to Python versio…