Brian Lee <[email protected]> added the comment:
Thanks for clarifying - I see now that the docs specifically call out the lack
of guarantees here with "usually but not always regard them as equivalent".
I did want to specifically explain the context of my bug;
1. NumPy's strings have some unexpected behavior because they have fixed-length
strings (represented inline) and var-length strings (which are pointers to
Python strings). Various arcana dictate which version you get, and wrappers
like pandas.read_csv can also throw a wrench in the mix. It is quite easy for
the nominal "string type" to change from under you, which is how I stumbled on
this bug.
2. I was using functools.cache as a way to intern objects and short-circuit
otherwise very expensive equality calculations by reducing them to pointer
comparisons - hence my desire for exact cache hits when typed=False.
While I agree this is Working As Documented, it does not Work As Expected in my
opinion. I would expect the stdlib optimized implementation to follow the same
behavior as this naive implementation, which does consider "hello world" and
np.str_("hello world") to be equivalent.
def cache(func):
_cache = {}
@functools.wraps(func)
def wrapped(*args, **kwargs):
cache_key = tuple(args) + tuple(kwargs.items())
if cache_key not in _cache:
_cache[cache_key] = func(*args, **kwargs)
return _cache[cache_key]
return wrapped
----------
title: functools.lru_cache does not consider strings and numpy strings as
equivalent -> functools.lru_cache does not guarantee cache hits for equal values
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Python tracker <[email protected]>
<https://bugs.python.org/issue44992>
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