def counter(func):
"""
A decorator that counts and prints the number of times a function has been executed
"""
def wrapper(*args, **kwargs):
wrapper.count = wrapper.count + 1
res = func(*args, **kwargs)
print "{0} has been used: {1}x".format(func.__name__, wrapper.count)
return res
wrapper.count = 0
return wrapper
函数是对象所以可以为他添加属性，利用这个属性来记录次数
