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[Add test case] Bug in return type of deque.copy() in generic type #12641
Description
Bug Report
Mypy reasons incorrectly about the return type of collections.deque.copy() if the item type is a generic with a type parameter inside a generic class.
To Reproduce
from collections import deque
from typing import Any, Callable, Generic, List, Protocol, TypeVar
T = TypeVar("T")
def test(item_type: T) -> None:
a: deque[List[T]] = deque()
b: deque[List[T]] = a.copy() # ok
class Test(Generic[T]):
def test(self) -> None:
a: deque[List[T]] = deque()
b: deque[List[T]] = a.copy() # error: Incompatible types in assignment (expression has type "deque[List[List[T]]]", variable has type "deque[List[T]]") [assignment]Expected Behavior
The return type in the above example should be List[T] not List[List[T]].
Your Environment
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Mypy version used: 0.942
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Mypy command-line flags:
mypy test.py -
Mypy configuration options from
mypy.ini(and other config files):[tool.mypy] strict = true namespace_packages = true ignore_missing_imports = true show_error_codes = true exclude = "tests"
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Python version used: 3.10.2
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Operating system and version: OSX 12.2.1 Monterey
Activity
[-]Bug in return type of `deque.copy()` if type variables are involved[/-][+]Bug in return type of `deque.copy()` if generic type[/+][-]Bug in return type of `deque.copy()` if generic type[/-][+]Bug in return type of `deque.copy()` in generic type[/+]JelleZijlstra commentedon Apr 21, 2022
deque.copyin typeshed is justdef copy(self: Self) -> Self:, so I do think this is a bug in mypy. Does it reproduce on current master with #12590 applied?AlexWaygood commentedon Apr 21, 2022
I can reproduce with 0.942, but not with mypy master. The "first good commit" is indeed 20b0b9b -- so yep, #12590 fixed this.
JelleZijlstra commentedon Apr 21, 2022
Great, let's add a test case for this one too.
[-]Bug in return type of `deque.copy()` in generic type[/-][+][Add test case] Bug in return type of `deque.copy()` in generic type[/+]