Python类型的类联合及其实例答案

【问题标题】：Python typing Union of class and it's instancePython类型的类联合及其实例
【发布时间】：2017-12-09 04:33:35
【问题描述】：

说我有

class Foo:
   pass

我想编写一个可以接受 Foo 实例或某些 Foo 子类（不是实例）的函数。所以我写了

def bar(o: Union[Foo, Type[Foo]]):
    print(1)

并得到这样的错误：

TypeError                                 Traceback (most recent call last) <ipython-input-161-2a8355efa688> in <module>()
----> 1 def bar(o: Union[Foo, Type[Foo]]):
      2     print(1)
      3 

/usr/lib/python3.5/typing.py in __getitem__(self, parameters)
    550             parameters = (parameters,)
    551         return self.__class__(self.__name__, self.__bases__,
--> 552                               dict(self.__dict__), parameters, _root=True)
    553 
    554     def __eq__(self, other):

/usr/lib/python3.5/typing.py in __new__(cls, name, bases, namespace, parameters, _root)
    510                 continue
    511             if any(isinstance(t2, type) and issubclass(t1, t2)
--> 512                    for t2 in all_params - {t1} if not isinstance(t2, TypeVar)):
    513                 all_params.remove(t1)
    514         # It's not a union if there's only one type left.

/usr/lib/python3.5/typing.py in <genexpr>(.0)
    510                 continue
    511             if any(isinstance(t2, type) and issubclass(t1, t2)
--> 512                    for t2 in all_params - {t1} if not isinstance(t2, TypeVar)):
    513                 all_params.remove(t1)
    514         # It's not a union if there's only one type left.

/usr/lib/python3.5/typing.py in __subclasscheck__(self, cls)    1075   return True    1076                 # If we break out of the loop, the superclass gets a chance.
-> 1077         if super().__subclasscheck__(cls):    1078             return True    1079         if self.__extra__ is None or isinstance(cls, GenericMeta):

/home/alexey/dev/gcore/django/lib/python3.5/abc.py in
__subclasscheck__(cls, subclass)
    223                 return True
    224         # Check if it's a subclass of a subclass (recursive)
--> 225         for scls in cls.__subclasses__():
    226             if issubclass(subclass, scls):
    227                 cls._abc_cache.add(subclass)

TypeError: descriptor '__subclasses__' of 'type' object needs an argument

是不是无法在python中指定该类型，还是我使用了错误的方法？

【问题讨论】：

无法复制。既不使用 python 3.6 也不使用 python 3.5。

标签： python python-3.x type-hinting typing

【解决方案1】：

见typing/issue 266。此问题已得到修复，并且不再出现在 Python 的更新版本中。

使用 Python 3.6.1，函数编译良好，注释存储正确：

>>> def bar(o: Union[Foo, Type[Foo]]):
...     print(1)
>>> typing.get_type_hints(bar)
{'o': typing.Union[__main__.Foo, typing.Type[__main__.Foo]]}

【讨论】：