Type narrowing using "in tuple"

[yabirgb]

Mypy fails to recognize after a explicit check that a set of variables can't be None

To Reproduce

Run mypy on the following script

from typing import Optional

class Test:    
    def double(self, x: int) -> int:
        return x * 2

def check_value(a: Optional[Test], b: Optional[int]) -> Optional[int]:
    if None in (a, b):
        return None
    
    return a.double(b)
    
if __name__ == '__main__':
    check_value(Test(), 2)

Expected Behavior

The linter should not complain as after the if check both variables a and b can't be None.

Actual Behavior

The linter says that the None possibility for the variable lacks the method. Is not correct since we have
taken action to prevent this.

testmypy.py:11: error: Item "None" of "Optional[Test]" has no attribute "double"
testmypy.py:11: error: Argument 1 to "double" of "Test" has incompatible type "Optional[int]"; expected "int"

Your Environment

• Mypy version used: 0.931
• Mypy command-line flags: mypy testmypy.py
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: 3.9.10 and 3.7
• Operating system and version: EndeavourOS Linux x86_64 - 5.16.4-arch1-1

[erictraut]

The pattern None in (a, b) is not current supported for type narrowing by mypy. If you use the pattern a is None or b is None, it will work as expected.

[nunesvictor]

I have a similar problem. See, if I try to check if several elements are not None with all function, mypy ins't capable to infer the variable isn't Optional anymore. Example:

my_model: Optional[MyModel] = optionalDict.get('my_model')
my_second_model: Optional[MySecondModel] = optionalDict.get('my_second_model')

if not all([my_model, my_second_model]):
    raise BaseException('Models cannot be None')

my_model.attr # <--- still infers like Optional[MyModel]

[JelleZijlstra]

Duplicate of #3229