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lru_cache doesn't work well with properties #2569
Description
I have following code:
#! /usr/bin/env python
import time
from functools import lru_cache
class MyClass:
@property
@lru_cache(1)
def expensive_operation(self) -> int:
time.sleep(2)
return 42
def another_operation(self) -> int:
return self.expensive_operation + 1
if __name__ == '__main__':
o = MyClass()
print(o.expensive_operation)
print(o.expensive_operation)
print(o.another_operation())It works as expected:
$ ./test.py
42
42
43
Yet, mypy is showing errors:
$ mypy test.py
test.py:7: error: Decorated property not supported
test.py:14: error: Unsupported operand types for + ("_lru_cache_wrapper[int]" and "int")
The lru_cache works just fine when decorated as property, and the returned type should be int and not _lru_cache_wrapper[int].
This is on python 3.7.0 and mypy 0.641.
Activity
JelleZijlstra commentedon Oct 29, 2018
I doubt this can be fixed in typeshed ("Decorated property not supported" is a mypy limitation). You'll have to go to mypy.