mypy：不兼容的返回值类型

Question

所以，我有一个数据类如下

@dataclass
class DataObj:
    """ DataObj creates an object for each record in data
    """
    name: str
    profit: int
    space: float

我有另一个容器 class 包含上述 class 的对象

class DataContainer:
    """ Data Container class holding objects of DataObj class
    """
    def __init__(self, data_tuple_list: List[Tuple[str, int, float]]) -> None:
        self.container = []
        for data_tuple in data_tuple_list:
            self.container.append(DataObj(*data_tuple))

    def __getitem__(self, n: int) -> Type[DataObj]:
        return self.container.__getitem__(n)

但是，当我使用 mypy 检查代码时，出现以下错误

error: Incompatible return value type (got "DataObj", expected "Type[DataObj]")
Found 1 error in 1 file (checked 1 source file)

我的 python 版本是3.8.10 。

问题：如何修复错误。

编辑

1. 如果我使用self.container: List[DataObj] = [] ，我得到error: Incompatible return value type (got "DataObj", expected "Type[DataObj]") Found 1 error in 1 file (checked 1 source file)
2. 如果我使用self.container: List[Type[DataObj]] = [] ，我会得到error: Argument 1 to "append" of "list" has incompatible type "DataObj"; expected "Type[DataObj]" Found 1 error in 1 file (checked 1 source file) error: Argument 1 to "append" of "list" has incompatible type "DataObj"; expected "Type[DataObj]" Found 1 error in 1 file (checked 1 source file) 。

Answer 1

您可能也没有键入提示您的容器（ self.container ），所以 mypy 将其视为List[Any]并且可能看不到它仅包含DataObj类型的值，因此当您从列表，mypy 不能确定它是DataObj类型的东西

尝试：

class DataContainer:
    """ Data Container class holding objects of DataObj class
    """
    def __init__(self, data_tuple_list: List[Tuple[str, int, float]]) -> None:
        self.container: List[DataObj] = [
            DataObj(*data_tuple)
            for data_tuple in data_tuple_list
        ]

    def __getitem__(self, n: int) -> Type[DataObj]:
        return self.container[n]

编辑

这是我尝试过的，它对我有用：

from dataclasses import dataclass
from typing import List, Tuple


@dataclass
class DataObj:
    """ DataObj creates an object for each record in data
    """
    name: str
    profit: int
    space: float


class DataContainer:
    """ Data Container class holding objects of DataObj class
    """

    def __init__(self, data_tuple_list: List[Tuple[str, int, float]]) -> None:
        self.container = [
            DataObj(*data_tuple)
            for data_tuple in data_tuple_list
        ]

    def __getitem__(self, n: int) -> DataObj:
        return self.container[n]

if __name__ == '__main__':
    data_tuple_list_concrete = [
        ('test1', 1, 1.1),
        ('test2', 2, 2.2),
        ('test3', 3, 3.3),
        ('test4', 4, 4.4),
        ('test5', 5, 5.5),
    ]

    dc = DataContainer(data_tuple_list_concrete)
    print(dc[0])
    print(dc[1])
    print(dc[2])
    print(dc[3])
    print(dc[4])

"""
Output:

DataObj(name='test1', profit=1, space=1.1)
DataObj(name='test2', profit=2, space=2.2)
DataObj(name='test3', profit=3, space=3.3)
DataObj(name='test4', profit=4, space=4.4)
DataObj(name='test5', profit=5, space=5.5)
"""

$ mypy main.py
Success: no issues found in 1 source file