Mypy misunderstands class-level namespace (spurious `Variable "module.Class.attribute" is not valid as a type`)

首先使用 mypy 运行提供的 Python 示例，并比较名为 dict 的类属性与后续 d:dict 注解的诊断结果。当该示例不再报告多余的 "not valid as a type" 错误，同时保留所述的注解行为时，即表示完成。

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.