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Description
Bug Report
Mypy seems to bind the TypeVar of a Generic decorator incorrectly when a variable is annotated as a Union.
To Reproduce
This example is based on this untyped cython code.
from typing import Callable, Generic, Optional, TypeVar, Union, overload
F = TypeVar("F")
G = TypeVar("G")
class cache_readonly(Generic[F, G]):
def __init__(self, func: Callable[[F], G]) -> None:
self.func = func
self.name = func.__name__
self.__doc__ = getattr(func, "__doc__", None)
@overload
def __get__(self, obj: F, typ) -> G:
...
@overload
def __get__(self, obj: None, typ) -> "cache_readonly[F, G]":
...
def __get__(self, obj: Optional[F], typ) -> Union[G, "cache_readonly[F, G]"]:
if obj is None:
# accessed on the class, not the instance
return self
# Get the cache or set a default one if needed
cache = getattr(obj, "_cache", None)
if cache is None:
cache = obj._cache = {} # type: ignore
if self.name in cache:
val = cache[self.name]
else:
val = self.func(obj)
cache[self.name] = val
return val
def __set__(self, obj: F, value: G) -> None:
raise AttributeError("Can't set attribute")
class TestA:
@cache_readonly
def x(self) -> str:
return "A"
class TestB:
@cache_readonly
def x(self) -> str:
return "B"
def test(obj: Union[TestA, TestB]) -> str:
return obj.x
Expected Behavior
Mypy and pyright are happy with the code :)
Actual Behavior
mypy
test.py:55: error: Argument 1 to "__get__" of "cache_readonly" has incompatible type "Union[TestA, TestB]"; expected "TestA"
test.py:55: error: Argument 1 to "__get__" of "cache_readonly" has incompatible type "Union[TestA, TestB]"; expected "TestB"
Pyright doesn't complain (except for the __doc__
line).
Your Environment
- Mypy version used: 0.910
- Mypy command-line flags: -
- Mypy configuration options from
mypy.ini
(and other config files): - - Python version used: 3.9.6
- Operating system and version: CentOS 3.10.0-693.5.2.el7.x86_64