装饰器的应用

请设计一个decorator，它可作用于任何函数上，并打印该函数的执行时间：

import time,functools
def metric(fn):
    @functools.wraps(fn)
    def wrapper(*args, **kw):
        start = time.time()
        result = fn(*args, **kw)
        end = time.time()
        print('%s executed in %s ms' % (fn.__name__, (end - start) * 1000))
        return result
    return wrapper
    
@metric
def fast(x,y):
    time.sleep(0.0012)
    return x+y
    
@metric
def slow(x,y):
    time.sleep(0.1234)
    return x*y
    
f = fast(1, 2)
s = slow(1, 2)
if f != 3:
    print('Fail')
elif s != 2:
    print('Fail')