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List[Literal[...]] type being narrowed where it shouldn't be #9850
Description
Bug Report
Adding an if check on a specific index of a List of Literals seems to narrow down its scope, even though the list can be modified and the value at that index can change.
To Reproduce
Run mypy over this piece of code:
foo: List[Literal['a', 'b']] = ['a', 'b', 'a']
if foo[0] == 'a':
print('a')
exit()
foo.pop(0)
reveal_type(foo[0])
if foo[0] == 'a':
passExpected Behavior
Revealed type to be Literal['a', 'b'], and the conditional to be valid.
Actual Behavior
t.py:11: note: Revealed type is 'Literal['b']'
t.py:12: error: Non-overlapping equality check (left operand type: "Literal['b']", right operand type: "Literal['a']")Your Environment
- Mypy version used: 0.790
- Mypy command-line flags:
--strict - Python version used: 3.9.1 64-bit
- Operating system and version: Fedora 33 x86_64
Activity
tusharsadhwani commentedon Dec 30, 2020
Even doing:
It seems to think that the type of
list[index]can't change once narrowed down.tusharsadhwani commentedon Dec 5, 2021
^ Reproduces on mypy 0.910 as well.