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Possible regression when narrowing using isinstance #16462
Description
Bug Report
Type narrowing using isinstance with 1.7 behaves differently from 1.6 for seemingly valid code.
To Reproduce
import typing
class A:
def write(self) -> str:
return "A"
# succeeds
def eq1(self, other: typing.Any) -> bool:
if other:
if isinstance(other, self.__class__):
return self.write() == other.write()
return False
# fails
def eq2(self, other: typing.Any) -> bool:
if other and isinstance(other, self.__class__):
return self.write() == other.write()
return FalseExpected Behavior
The eq1 and eq2 should both be valid code. eq2 fails under 1.7 but succeeded under 1.6.
Actual Behavior
file.py:15: error: Returning Any from function declared to return "bool" [no-any-return]
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used: 1.7.0
- Mypy command-line flags:
- Mypy configuration options from
mypy.ini(and other config files):
# Global options:
[mypy]
ignore_missing_imports = True
follow_imports = silent
strict = True
- Python version used:
Python 3.12 macos-arm64
Activity
ilevkivskyi commentedon Nov 11, 2023
Yeah, most likely I did this.
Anywith type narrowing works quite arbitrary (and it was never really consistent). It actually works for flipped order (i.e.if isinstance(other, self.__class__) and other: ...). I will check if it is easy to make it more consistent (or at least return the old behavior) without causing troubles in other places.cmeyer commentedon Nov 11, 2023
I'm already changing my code to use only the
isinstancecheck. The first clause (other) is redundant sinceNonecannot ever pass theisinstancecheck anyway. Thanks for all of your other work.Narrow Any in and_conditional_map (python#21167)