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Improved lru_cache which keeps argument types - #3880

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Improved lru_cache which keeps argument types#3880
asottile wants to merge 1 commit into
python:masterfrom
asottile:improved_lru_cache

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@asottile asottile commented Mar 23, 2020

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see also python/mypy#5107

demo file

from functools import lru_cache

@lru_cache(maxsize=5)
def f(x: int) -> int:
    return 6 * x

reveal_type(f)
reveal_type(f.__wrapped__)
reveal_type(f(1))
f('wat')  # should be an error

before

$ mypy t.py
t.py:7: note: Revealed type is 'functools._lru_cache_wrapper[builtins.int*]'
t.py:8: note: Revealed type is 'def (*Any, **Any) -> builtins.int*'
t.py:9: note: Revealed type is 'builtins.int*'

after

$ mypy --custom-typeshed-dir typeshed t.py
t.py:7: note: Revealed type is 'functools._lru_cache_wrapper[def (x: builtins.int) -> builtins.int]'
t.py:8: note: Revealed type is 'def (x: builtins.int) -> builtins.int'
t.py:9: note: Revealed type is 'builtins.int'
t.py:10: error: Argument 1 to "f" has incompatible type "str"; expected "int"
Found 1 error in 1 file (checked 1 source file)

@asottile asottile mentioned this pull request Mar 23, 2020
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@asottile

asottile commented Mar 23, 2020

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this also (?) appears to fix generics and lru_cache:

demo

from typing import TypeVar
from functools import lru_cache

T = TypeVar('T')

@lru_cache(maxsize=5)
def f(x: T) -> T: ...

reveal_type(f)
reveal_type(f.__wrapped__)
reveal_type(f(1))
reveal_type(f('wat'))

before

$ mypy t.py
t.py:9: note: Revealed type is 'functools._lru_cache_wrapper[T`-1]'
t.py:10: note: Revealed type is 'def (*Any, **Any) -> T`-1'
t.py:11: note: Revealed type is 'T`-1'
t.py:12: note: Revealed type is 'T`-1'

after

$ mypy t.py --custom-typeshed-dir typeshed
t.py:9: note: Revealed type is 'functools._lru_cache_wrapper[def [T] (x: T`-1) -> T`-1]'
t.py:10: note: Revealed type is 'def [T] (x: T`-1) -> T`-1'
t.py:11: note: Revealed type is 'builtins.int*'
t.py:12: note: Revealed type is 'builtins.str*'

@asottile

asottile commented Mar 23, 2020

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ah dang, doesn't work for classes:

from functools import lru_cache

class C:
    @lru_cache(maxsize=5)
    def f(self, x: int) -> int: ...

reveal_type(C().f)
reveal_type(C().f(1))
C().f('wat')
$ mypy t.py --custom-typeshed-dir typeshed
t.py:7: note: Revealed type is 'functools._lru_cache_wrapper[def (self: t.C, x: builtins.int) -> builtins.int]'
t.py:8: error: Too few arguments for "f" of "C"
t.py:8: note: Revealed type is 'builtins.int'
t.py:8: error: Argument 1 to "f" of "C" has incompatible type "int"; expected "C"
t.py:9: error: Too few arguments for "f" of "C"
t.py:9: error: Argument 1 to "f" of "C" has incompatible type "str"; expected "C"
Found 4 errors in 1 file (checked 1 source file)

@asottile asottile closed this Mar 23, 2020
@asottile
asottile deleted the improved_lru_cache branch March 23, 2020 22:49
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