Mypy无法识别具有继承的类类型

问题描述

我无法让Mypy在这里识别正确的类型。我要做的就是为类创建一个dict的名称，因此我可以通过提供type_name作为其属性来获取该类。也许是因为dataclass和dataclasses-json的东西引起了混淆？

# mypy_test.py

from dataclasses import dataclass
from typing import Any,Dict,Type,TypeVar

from dataclasses_json import DataClassJsonMixin


@dataclass
class _BaseDataItem(DataClassJsonMixin):
    name: str  # functions as an ID. Subclasses should NOT modify its value after creation.
    type_name: str
    body: Any = None
    # etc ...


@dataclass
class DatanetItem(_BaseDataItem):
    type_name: str = "datanet"


@dataclass
class RedshiftItem(_BaseDataItem):
    type_name: str = "redshift"


# https://mypy.readthedocs.io/en/stable/kinds_of_types.html#the-type-of-class-objects
IT = TypeVar("IT",bound=_BaseDataItem)

items2classes: Dict[str,Type[IT]] = {
    c.type_name: c for c in (DatanetItem,RedshiftItem)
}


def create_obj(name: str,item_type: str) -> _BaseDataItem:
    klass = items2classes[item_type]
    obj = klass(name)
    return obj

用法示例：

In [1]: import mypy_test as m

In [2]: m.create_obj('123','datanet')
Out[2]: DatanetItem(name='123',type_name='datanet',body=None)

In [3]: m.create_obj('mytable','redshift')
Out[3]: RedshiftItem(name='mytable',type_name='redshift',body=None)

尽管我以为我遵循了in the docs的说明，但由于某些原因，MyPy一直给我这个错误：

mypy_test.py:28: error: Type variable "mypy_test.IT" is unbound
mypy_test.py:28: note: (Hint: Use "Generic[IT]" or "Protocol[IT]" base class to bind "IT" inside a class)
mypy_test.py:28: note: (Hint: Use "IT" in function signature to bind "IT" inside a function)
mypy_test.py:35: error: Cannot instantiate type "Type[IT?]"
Found 2 errors in 1 file (checked 1 source file)

解决方法

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mypy python python-dataclasses