如何注释属于类对象的类型(而不是类实例)? [英] How to annotate a type that's a class object (instead of a class instance)?

问题描述

注释需要一个类对象而不是该类实例的函数参数的正确方法是什么?

What is the proper way to annotate a function argument that expects a class object instead of an instance of that class?

在下面的示例中，some_class参数应该是类型实例(它是一个类)，但是这里的问题是type的范围太广:

In the example below, some_class argument is expected to be a type instance (which is a class), but the problem here is that type is too broad:

def construct(some_class: type, related_data:Dict[str, Any]) -> Any:
    ...

在some_class需要一组特定类型的对象的情况下，使用type根本没有帮助. typing模块可能需要执行以下操作的Class泛型:

In the case where some_class expects a specific set of types objects, using type does not help at all. The typing module might be in need of a Class generic that does this:

def construct(some_class: Class[Union[Foo, Bar, Baz]], related_data:Dict[str, Any]) -> Union[Foo, Bar, Baz]:
    ...

在上面的示例中，some_class是Foo，Bar或Faz类，而不是其实例.它们在类树中的位置无关紧要，因为some_class: Class[Foo]也应该是有效的情况.因此，

In the example above, some_class is the Foo, Bar or Faz class, not an instance of it. It should not matter their positions in the class tree because some_class: Class[Foo] should also be a valid case. Therefore,

# classes are callable, so it is OK
inst = some_class(**related_data)

或

# instances does not have __name__
clsname = some_class.__name__

或

# an operation that only Foo, Bar and Baz can perform.
some_class.a_common_classmethod()

对于mypy，pytype，PyCharm等应该没问题.

should be OK to mypy, pytype, PyCharm, etc.

如何使用当前的实现(Python 3.6或更早版本)来完成此操作?

How can this be done with current implementation (Python 3.6 or earlier)?

推荐答案

要注释作为类的对象，请使用

To annotate an object that is a class, use typing.Type. For example, this would tell the type checker that some_class is class Foo or any of its subclasses:

from typing import Type
class Foo: ...
class Bar(Foo): ...
class Baz: ...
some_class: Type[Foo]
some_class = Foo # ok
some_class = Bar # ok
some_class = Baz # error
some_class = Foo() # error

请注意，Type[Union[Foo, Bar, Baz]]和Union[Type[Foo], Type[Bar], Type[Baz]]完全等效.

如果some_class可以是许多类中的任何一个，则可能要使它们全部继承自相同的基类，并使用Type[BaseClass].请注意，目前该继承必须是非虚拟的(关于虚拟继承的mypy支持为正在讨论).

If some_class could be any of a number of classes, you may want to make them all inherit from the same base class, and use Type[BaseClass]. Note that the inheritance must be non-virtual for now (mypy support for virtual inheritance is being discussed).

经过编辑以确认是否允许使用Type[Union[....

Edited to confirm that Type[Union[... is allowed.

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