参数注释，只是注释，不会自动做类型验证

    1. def hello(name: str, age: int=20):
    2.     print(f'hello {name}, your age is {age}.')
    4. hello.__annotations__
    5. # {'name': <class 'str'>, 'age': <class 'int'>}

    返回值注释

    1. def hello() -> None:
    2.     print('hello world!')
    4. hello.__annotations__    # {'return': None}
    6. def square(num: int) -> int:
    7.     return num * num
    9. square.__annotations__    # {'num': <class 'int'>, 'return': <class 'int'>}
    11. help(square)    # square(num:int) -> int

    inspect 模块，可获取函数的参数注释和返回值注释信息

    1. import inspect
    3. sig = inspect.signature(square)
    5. sig.parameters    # mappingproxy(OrderedDict([('num', <Parameter "num:int">)]))
    7. sig.return_annotation    # <class 'int'>

    结合上面参数注释和 inspect 模块的用法，就可以编写一个用来检查函数参数的装饰器了

    1. import inspect
    2. import functools
    5. class ParamTypeError(Exception):
    6.     pass
    9. def validate_parameters(func):
    10.     @functools.wraps(func)
    11.     def wrap(*args, **kwargs):
    12.         sig = inspect.signature(func)
    13.         for arg, param in zip(list(args) + list(kwargs.keys()), sig.parameters.values()):
    14.             if param.annotation != inspect._empty:
    15.                 if not isinstance(arg, param.annotation):
    16.                     raise ParamTypeError('parameter type error', 'expect {} but got {}'.format(param.annotation, type(arg)))
    17.         return func(*args, **kwargs)
    18.     return wrap
    21. @validate_parameters
    22. def hello(name, age:int=20):
    23.     print(f'hello {name}, age is {age}.')
    26. if __name__ == '__main__':
    27.     hello('world')
    28.     hello('world', age=[1, 2, 3])
    29.     # __main__.ParamTypeError: ('parameter type error', "expect <class 'int'> but got <class 'str'>")