9-3定义带参数的装饰器

# -*- coding:utf-8 -*-

'''带参数的装饰器，也就是根据参数定制化一个装饰器，可以看成生产装饰器的工厂
   每次调用 typeassert，返回一个特定的装饰器，然后用它去装饰其它函数   '''

from inspect import signature
# 提取函数签名，只有在python3.5有该模块

def typeassert(*ty_args, **ty_kargs):
    def decorator(func):
        # func -> a, b
        # d = {'a':int, 'b':str}
        sig = signature(func)
        btypes = sig.bind_partial(*ty_args, **ty_kargs).arguments
        # 得到类型关系的映射,下面是bind_partial函数的注释
        # Get a BoundArguments object, that partially maps the passed `args` and `kwargs` to the function's signature.
        # Raises `TypeError` if the passed arguments can not be bound.

        def wrapper(*args, **kargs):
            # arg in d, instance(arg, d[arg])
            for name, obj in sig.bind(*args, **kargs).arguments.items():
                if name in btypes:
                    if not isinstance(obj, btypes[name]):
                        raise TypeError('"%s" must be "%s"' % (name, btypes[name]))
            return func(*args, **kargs)
        return wrapper
    return decorator


@typeassert(int, str, list)
def f(a, b, c):
    print(a, b, c)

f(1, 'abc', [1, 2, 3])
f(1, 2, [1, 2, 3])