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Description
Consider the following:
from typing import Any
@dataclass
class C:
dict:object # This attribute name shadows `dict` type, but it should not shadow the name inside of the `class` lexical scope; that's not how python works.
d:dict # This attribute is annotated as `dict`. The interpreter does not pick up the previous shadowed attribute, but mypy does.
c = C(dict={'a':1}, d={'b':2})
print(c.__annotations__)
assert c.__annotations__['d'] is dict # This proves that mypy is misunderstanding the name `dict`.
mypy 0.942 output:
$ mypy property_name_shadows_type.py
property_name_shadows_type.py:11: error: Variable "property_name_shadows_type.C.dict" is not valid as a type
property_name_shadows_type.py:11: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
Found 1 error in 1 file (checked 1 source file)
Ill-advised as this naming may seem, mypy is making a semantic mistake here. The dict:object
line should not alter the namespace in which d:dict
is evaluated (I hope that's the correct terminology!). I ran across this case when a machine-generated dataclass used a builtin type name for an attribute name.
Some notes:
- This is not specific to
dict
; it happens for all builtin type names as well as imported type names. - If you change the first declaration to
dict:Any
, then the problem goes away. This seems indicative of a deeper problem in mypy. - Whether or not the class is decorated as dataclass seems irrelevant; it's just here for ease of constructing the example instance.