python 3.5+中的类型提示克隆函数

Question

假设我有以下课程：

class Parent:
    def clone_self(self) -> 'Parent':
        clone = self.__class__()
        # Initialize clone here.
        return clone

    def clone_with_class(self, klass: Type['Parent']) -> 'Parent':
        clone = klass()
        # Initialize clone here.
        return clone

class Child(Parent):
    def child_method(self) -> None:
        pass

有什么方法可以让类型更具体吗？我希望能够说：

child = Child()
clone = child.clone_self()
clone.child_method()

clone = child.clone_with_class(Child)
clone.child_method()

但是，正如所写，这不会通过类型检查，因为克隆被认为是Parent 类型而不是Child。

我尝试使用TypeVar，但这似乎不起作用 - 至少在 PyCharm 中，因为当我尝试调用构造函数时它抱怨该类型不可调用，可能是因为它涉及前向引用，而 PyCharm 是迷糊了。

Entity = TypeVar('Entity', bound='Parent')
class Parent:
    def clone_self(self) -> ???:
        clone = self.__class__()
        # initialize clone here
        return clone

    def clone_with_class(self, klass: Type[Entity]) -> Entity:
        clone = klass()
        # initialize clone here
        return clone

clone_with_class 的解决方案是否正确？也许 PyCharm 是错误的抱怨？否则，需要做什么来修复上面的代码？

应该是TypeVar('Entity', bound='Parent') 还是TypeVar('Entity', 'Parent')？

我发现的另一个解决方案是插入断言，虽然看起来有些难看：

child = Child()
parent = Parent()

clone = child.clone_self()
clone.child_method()  # should work

clone = child.clone_with_class(Child)
clone.child_method()  # should work

clone = parent.clone_with_class(Child)
clone.child_method()  # should work

clone2 = parent.clone_self()
clone2.child_method()  # should be an error

clone2 = parent.clone_with_class(Parent)
clone2.child_method()  # should be an error

clone2 = child.clone_with_class(Parent)
clone2.child_method()  # Should be an error

一旦我很好地理解了什么是正确的，我就可以在 PyCharm 错误地抱怨时向它提交错误。

根据建议的答案，我尝试使用 mypy：

from typing import TypeVar, Type

Entity = TypeVar('Entity', bound='Parent')
class Parent:
    def clone_self(self: Entity) -> Entity:
        clone = type(self)()
        # initialize clone here
        return clone

    def clone_with_class(self, klass: Type[Entity]) -> Entity:
        clone = klass()
        # initialize clone here
        return clone

class Child(Parent):
    def child_method(self) -> None:
        print("Calling child method")

child = Child()
parent = Parent()

clone = child.clone_self()
clone.child_method()  # should work

clone = child.clone_with_class(Child)
clone.child_method()  # should work

clone = parent.clone_with_class(Child)
clone.child_method()  # should work

clone2 = parent.clone_self()
clone2.child_method()  # should be an error

clone2 = parent.clone_with_class(Parent)
clone2.child_method()  # should be an error

clone2 = child.clone_with_class(Parent)
clone2.child_method()  # Should be an error

我得到以下信息：

$ mypy --strict test.py
test.py:32: error: "Parent" has no attribute "child_method"
test.py:35: error: "Parent" has no attribute "child_method"
test.py:38: error: "Parent" has no attribute "child_method"

这些错误是预期的。

Answer 1

我不知道 PyCharm 目前是否接受这个，但以下代码适用于 mypy：

from typing import TypeVar, Type

Entity = TypeVar('Entity', bound='Parent')
class Parent:
    def clone_self(self: Entity) -> Entity:
        clone = self.__class__()
        # initialize clone here
        return clone

    def clone_with_class(self, klass: Type[Entity]) -> Entity:
        clone = klass()
        # initialize clone here
        return clone

class Child(Parent):
    def child_method(self) -> None:
        print("Calling child method")

child = Child()
clone = child.clone_self()
clone.child_method()

clone = child.clone_with_class(Child)
clone.child_method()

请注意，我为self 指定了clone_self 的特定类型——这让我们可以根据需要更精确地键入返回类型。您可以在此处了解有关使用通用 self 的更多信息：http://mypy.readthedocs.io/en/stable/generics.html#generic-methods-and-generic-self

您的clone_with_class 方法也有一个错误，这可能会造成混淆——您忘记包含self 参数。