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我试图了解类型提示在 Python 中是如何工作的——尤其是在儿童类中。我在处理一个项目时遇到了这个问题，并且能够在一个示例中重新创建该问题，如下所示。

环境：

  • 蟒蛇：3.9.7
  • 我的：0.910
  • 操作系统：Ubuntu 20.04

示例代码：

from typing import List
import math

class Shape:
    def area(self):
        ...
    def perimeter(self):
        ...

class Circle(Shape):
    def __init__(self, r):
        self.r = r

    def area(self):
        return math.pi * self.r * self.r

    def perimeter(self):
        return 2 * math.pi * self.r

class Cube(Shape):
    def __init__(self, x):
        self.x = x
        self.corners = 4

    def area(self):
        return self.x * self.x

    def perimeter(self):
        return self.x * 4

class A:
    
    def __init__(self, element: Shape):
        self.element = element

class B(A):

    def __init__(self, element: Cube):
        super().__init__(element)

我不明白如何解决这个问题：

class AList:
    
    def __init__(self, elements: List[Shape]):
        self.elements = elements

class BList(AList):

    def __init__(self, elements: List[Cube]):
        super().__init__(elements) # This line is causing the Pyright error

        print([x.corners for x in elements])

BList我在课堂上收到以下 Pyright 错误super().__init__(elements)：

[Pyright reportGeneralTypeIssues] [E] Argument of type "List[Cube]" cannot be assigned to parameter "elements" of type "List[Shape]" in function "__init__" TypeVar "_T@list" is invariant "Cube" is incompatible with "Shape"

我还在 mypy 中收到以下错误消息：

(pymmdt) eduardo@avocado-MS-7C83:~/Downloads$ mypy example.py
example.py:49: error: Argument 1 to "__init__" of "AList" has incompatible type "List[Cube]"; expected "List[Shape]"
example.py:49: note: "List" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
example.py:49: note: Consider using "Sequence" instead, which is covariant
Found 1 error in 1 file (checked 1 source file)

将继续努力，但任何建议/反馈将不胜感激。感谢您的时间！

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0 回答 0