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Unpacking enum type generates an error #14782

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eltoder opened this issue Feb 26, 2023 · 0 comments · Fixed by #14827
Closed

Unpacking enum type generates an error #14782

eltoder opened this issue Feb 26, 2023 · 0 comments · Fixed by #14827
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bug mypy got something wrong topic-enum topic-metaclasses

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@eltoder
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eltoder commented Feb 26, 2023

To Reproduce

from enum import Enum

class E(Enum):
    A = 1
    B = 2

A, B = E

Actual Behavior

This code generates an error:

$ mypy --strict proj/iter_enum.py
proj/iter_enum.py:7: error: "Type[E]" object is not iterable  [misc]

Expected Behavior

This should type check without errors. Note that mypy knows that E is actually iterable. For example,

A, B = list(E)

works fine and so does iterating over E in a for loop.

Your Environment

  • Mypy version used: mypy 1.1.0+dev.c23e831ab0e7ec827c38cc830d3ebd3f4c43cd75
  • Mypy command-line flags: with and without --strict
  • Python version used: 3.10.6
@eltoder eltoder added the bug mypy got something wrong label Feb 26, 2023
This was referenced Feb 28, 2023
Closed
Merged
JukkaL pushed a commit that referenced this issue Mar 6, 2023
@AlexWaygood
Allow iterable class objects to be unpacked (including enums) (#14827)
b6cb0ed 
Fixes #14782

Currently, mypy issues a false positive if you try to unpack an enum
class:

```python
from enum import Enum

class E(Enum):
    A = 1
    B = 2

A, B = E  #  error: "Type[E]" object is not iterable  [misc]
```

This is because of a more general problem with class objects that have
`__iter__` defined on their metaclass. Mypy issues a false positive on
this code, where `Foo` is iterable by virtue of having `Meta` as its
metaclass:

```python
from typing import Iterator
class Meta(type):
    def __iter__(cls) -> Iterator[int]:
        yield from [1, 2, 3]

class Foo(metaclass=Meta): ...

a, b, c = Foo  # error: "Type[Foo]" object is not iterable  [misc]
reveal_type(a)  # error: Cannot determine type of "a"  [has-type]  # note: Revealed type is "Any"
```

This PR fixes the false positive with enums, and the more general false
positive with iterable class objects.
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Allow iterable class objects to be unpacked (including enums) AlexWaygood/mypy
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@eltoder @AlexWaygood