mypy incorrectly infers type of ClassVar when accessed in try/except AttributeError

[gswifort]

mypy incorrectly infers type of ClassVar when accessed in try/except AttributeError

Bug Report

What's wrong

When accessing a ClassVar annotated variable inside a try/except AttributeError block, mypy incorrectly infers the type of the variable, leading to false positive type errors.

How to reproduce

import enum
import typing as t


class MyEnum(float, enum.Enum):
    """Example enum that has a cached class variable."""
    
    if t.TYPE_CHECKING:
        _cache: t.ClassVar[dict[str, "MyEnum"]]
    
    VALUE_A = 1.0
    VALUE_B = 2.0
    
    @classmethod
    def from_string_broken(cls, key: str) -> "MyEnum":
        """This method shows the mypy type inference bug."""
        try:
            # mypy incorrectly thinks cls._cache is MyEnum instead of dict[str, MyEnum]
            cache = cls._cache
        except AttributeError:
            cache = {item.name: item for item in cls}
            cls._cache = cache
        
        return cache[key]

Actual behavior

mypy reports these errors:

error: Incompatible types in assignment (expression has type "dict[str, MyEnum]", variable has type "MyEnum")
error: Incompatible types in assignment (expression has type "MyEnum", variable has type "dict[str, MyEnum]") 
error: Value of type "MyEnum" is not indexable

Expected behavior

mypy should recognize that cls._cache has type dict[str, MyEnum] as declared in the ClassVar annotation, and not report any type errors.

Environment

• mypy version: 1.17.0
• Python version: 3.12.7

[sterliakov]

try/except is a read herring here, MRE:

import enum
from typing import ClassVar

class MyEnum(enum.Enum):
    _cache: ClassVar[str]
    
    VALUE_A = 1
    VALUE_B = 2
    
reveal_type(MyEnum._cache)  # N: Revealed type is "Literal[__main__.MyEnum._cache]?"