GeezerVison is showing github.com — contextlib.contextmanager allows `Iterator[T]` -- should probably be `Generator[T, None, None]`? · Issue #2772 · python/typeshed
contextlib.contextmanager allows Iterator[T] -- should probably be Generator[T, None, None]? #2772DescriptionFor instance, this script passes mypy:
import contextlib
from typing import Iterator
@contextlib.contextmanager
def f() -> Iterator[int]:
return iter([1])
with f():
pass
with f():
raise TypeError('wat')but fails at runtime (and not in the expected way):
$ python t.py
Traceback (most recent call last):
File "t.py", line 14, in <module>
raise TypeError('wat')
TypeError: wat
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "t.py", line 14, in <module>
raise TypeError('wat')
File "/usr/lib/python3.6/contextlib.py", line 99, in __exit__
self.gen.throw(type, value, traceback)
AttributeError: 'list_iterator' object has no attribute 'throw'Reacted by Ganden Schaffner, Cal Jacobson, Guido Imperiale, Thomas Grainger and Roman Donchenko Activitysrittau commented on Jan 30, 2019 graingert commented on Jun 30, 2021 contextlib.contextmanager doesn't need to be as specific as Generator[T, None, None], it could take the slightly wider type:
class ContextManagerArgReturnType(Protocol, Generic[T]):
def __next__(self) -> T: ...
def throw(self, exctype: Optional[Type[BaseException]], excinst: Optional[BaseException], exctb: Optional[TracebackType]) -> Any: ...
ContextManagerArgType = Callable[[], ContextManagerArgReturnType[T]]asottile commented on Mar 1, 2022 ContributorAuthor More actions this (unfortunately) caused a production incident today -- any chance this can be reconsidered (despite the backward incompatibility)? Reacted by Thomas Grainger Reacted by Iván || HacKan HacKanCuBa commented on Jun 2, 2022 So, this is an interesting pitfall of using Iterator[] instead of Generator[] as the docs suggest:
A generator can be annotated by the generic type Generator[YieldType, SendType, ReturnType]
...
Alternatively, annotate your generator as having a return type of either Iterable[YieldType] or Iterator[YieldType]
I'm just bumping this up. AlexWaygood commented on Jun 2, 2022
So, this is an interesting pitfall of using Iterator[] instead of Generator[] as the docs suggest:
A generator can be annotated by the generic type Generator[YieldType, SendType, ReturnType]
...
Alternatively, annotate your generator as having a return type of either Iterable[YieldType] or Iterator[YieldType]
I'm just bumping this up.
Can I ask why you're bumping it up? Did the current stubs mean that mypy failed to spot a bug in your code, the same as happened to @asottile? HacKanCuBa commented on Jun 3, 2022
So, this is an interesting pitfall of using Iterator[] instead of Generator[] as the docs suggest:
A generator can be annotated by the generic type Generator[YieldType, SendType, ReturnType]
...
Alternatively, annotate your generator as having a return type of either Iterable[YieldType] or Iterator[YieldType]
I'm just bumping this up.
Can I ask why you're bumping it up? Did the current stubs mean that mypy failed to spot a bug in your code, the same as happened to @asottile?
Which brought me here after reading a blogpost :D AlexWaygood commented on Nov 1, 2023 Marking as deferred unless/until PEP 696 is accepted, as per #7430 (comment). srittau commented on Feb 14, 2024 See #11422 for the type var generics feature tracker. hauntsaninja commented on Feb 20, 2024 Note that while PEP 696 will help some ergonomic issues and therefore could be good to re-assess, I'm still pretty strongly disinclined to change this. It's been 1.5 years since I commented in #7430 (comment) asking people to report real-life false negatives and no one else has (I just went through all the issues that link to this one and I don't remember any mypy issue reports either). A ruff lint with autofix could help, as would Jukka's suggestion here: #7430 (comment) Reacted by Alex Waygood Reacted by anthony sottile and James Hilton-Balfe max-muoto commented on Jul 13, 2024 Now that we have PEP 696, a PR experimenting with the effects here: #12334
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