False positive on manual overloaded `Foo[T].__init__(self, arg)` call
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bug
topic-overloads
- Dominant language
- Python
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Description
https://mypy-play.net/?mypy=latest&python=3.12&gist=8fb7e4ecda19d973ed94ee4487bc3ff9
from collections.abc import Sequence, Iterable
from typing import Never, overload
class Foo: ...
class Bar(Foo): ...
class FooSequence[F: Foo](Foo, Sequence[F]):
@overload
def __init__(self: "FooSequence[Never]", /) -> None: ...
@overload
def __init__(self, modules: Iterable[F], /) -> None: ...
def __init__(self, modules: Iterable[F] = (), /) -> None: ...
class BarSequence[B: Bar](Bar, FooSequence[B]):
def __init__(self, modules: Iterable[B] = (), /) -> None:
FooSequence[B].__init__(self, modules) # ❌️
main.py:17: error: Argument 1 to "__init__" of "FooSequence" has incompatible type "BarSequence[B]"; expected "FooSequence[Never]" [arg-type]
main.py:17: error: Argument 2 to "__init__" of "FooSequence" has incompatible type "Iterable[B]"; expected "Iterable[Never]" [arg-type]
This looks like a false positive to me; if the overloads are removed, it type checks without error: https://mypy-play.net/?mypy=latest&python=3.12&gist=ac42aa23c117ba5e2f2ea815a23cb134
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
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- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the error in main.py using the linked mypy-play example, then trace overload resolution for the explicit FooSequence[B].init(self, modules) call. Done means mypy accepts this call while retaining the overload behavior shown in the example.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 38/100