在UWP Windows 10应用程序上使用openCV(Using openCV on a UWP Windows 10 Application)

 对于尚未定义的Client类，可以使用字符串名称来使用前向引用 ： 
 
class Server():
    def register_client(self, client: 'Client')
        pass

You can use a forward reference by using a string name for the not-yet-defined Client class:
 
class Server():
    def register_client(self, client: 'Client')
        pass
 
As of Python 3.7, you can also postpone all runtime parsing of annotations by adding the following __future__ import at the top of your module:
 
from __future__ import annotations
 
at which point the annotations are stored as string representations of the abstract syntax tree for the expression; you can use typing.get_type_hints() to resolve those (and resolve forward references as used above).
 
See PEP 563 -- Postponed Evaluation of Annotations for details; this behaviour will be the default in Python 4.0.