Bug Report

mypy failed to narrow down union types includingSelf withisinstance.

To Reproduce

Consider the following code:

fromdataclassesimportdataclassfromtypingimportSelf,reveal_type@dataclassclassFoo:i:intdefbar(self,other:Self|int)->int:ifisinstance(other,Foo):returnself.i*other.ielse:reveal_type(other)# "int" expected, gets "Self | int"returnself.i*other# Unsupported operand types for * ("int" and "Self")  [operator]mypy(error)

Expected Behavior

Other should be infered as anint and mypy reports no error.

Actual Behavior

mypy failed to narrow type ofother

Revealed type is "Union[Self`0, builtins.int]"mypy(note)

Also, mypy reports the following error.

Unsupported operand types for * ("int" and "Self")  [operator]mypy(error)

Your Environment

• Mypy version used: 1.1.1
• Mypy command-line flags:--follow-imports=silent --ignore-missing-imports --show-column-numbers --no-pretty (VSCode defaults)
• Mypy configuration options frommypy.ini (and other config files): None
• Python version used: 3.11.1