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Invalid "Value of type Never is not indexable" #16468

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inducer opened this issue Nov 11, 2023 · 0 comments · Fixed by #16470
Closed

Invalid "Value of type Never is not indexable" #16468

inducer opened this issue Nov 11, 2023 · 0 comments · Fixed by #16470
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bug mypy got something wrong

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@inducer
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inducer commented Nov 11, 2023

To Reproduce

from typing import Union, Sequence


def f(pad_width: Union[int, Sequence[int]],) -> None:
    if (isinstance(pad_width, tuple)
          and len(pad_width) == 2
          and isinstance(pad_width[0], int)
          and isinstance(pad_width[1], int)
          ):
        pass

Expected Behavior

Type-checks fine.

Actual Behavior

mypy-bug.py:8: error: Value of type Never is not indexable  [index]
mypy-bug.py:9: error: Value of type Never is not indexable  [index]
Found 2 errors in 1 file (checked 1 source file)

Your Environment

  • Mypy version used: 1.7.0
  • Mypy command-line flags: none
  • Mypy configuration options from mypy.ini (and other config files): none
  • Python version used: 3.12
@inducer inducer added the bug mypy got something wrong label Nov 11, 2023
@ilevkivskyi ilevkivskyi mentioned this issue Nov 12, 2023
Merged
hauntsaninja pushed a commit that referenced this issue Nov 12, 2023
@ilevkivskyi
Fix missing meet case exposed by len narrowing (#16470)
efa5dcb 
Fixes #16468

The fix is straightforward.

Btw when fixing this I noticed that we disregard type arguments when
narrowing, for example:
```python
x: Sequence[int]
if isinstance(x, tuple):
    reveal_type(x)  # tuple[Any, ...], but should be `tuple[int, ...]`
```
I guess fixing this may be tricky, and it is quite old behavior.
@AlexWaygood AlexWaygood mentioned this issue Nov 13, 2023
Closed
@inducer inducer mentioned this issue Nov 14, 2023
Merged
JukkaL pushed a commit that referenced this issue Nov 22, 2023
@ilevkivskyi @JukkaL
Fix missing meet case exposed by len narrowing (#16470)
5c354c4 
Fixes #16468

The fix is straightforward.

Btw when fixing this I noticed that we disregard type arguments when
narrowing, for example:
```python
x: Sequence[int]
if isinstance(x, tuple):
    reveal_type(x)  # tuple[Any, ...], but should be `tuple[int, ...]`
```
I guess fixing this may be tricky, and it is quite old behavior.
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Fix missing meet case exposed by len narrowing ilevkivskyi/mypy
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@inducer