访问在装饰器之外的装饰器中创建的函数属性

Question

我想计算给定函数被调用的次数。

所以，我做了一个countcalls修饰器给我的功能__callcount属性，每增加一个电话。够简单。

我的问题是得到__callcount值后面退出。

这里是我的代码：

import functools 

def countcalls(f): 
    f.__callcount = 0 

    @functools.wraps(f) 
    def _countcalls(*args, **kwds): 
     f.__callcount += 1 
     print(' Called {0} time(s).'.format(f.__callcount)) 
     return f(*args, **kwds) 
    return _countcalls 

@countcalls 
def fib(n): 
    if n < 0: 
     raise ValueError('n must be > 0') 
    if n == 0 or n == 1: 
     return 1 

    return fib(n-1) + fib(n-2) 

if __name__ == '__main__': 
    print('Calling fib(3)...') 
    x = fib(3) 
    print('fib(3) = {0}'.format(x)) 

    print('Calling fib(3) again...') 
    x = fib(3) 
    print('fib(3) = {0}'.format(x)) 

    print('fib was called a total of {0} time(s).'.format(fib.__callcount)) 

产生以下输出（Python的3.3.0）：

Calling fib(3)... 
    Called 1 time(s). 
    Called 2 time(s). 
    Called 3 time(s). 
    Called 4 time(s). 
    Called 5 time(s). 
fib(3) = 3 
Calling fib(3) again... 
    Called 6 time(s). 
    Called 7 time(s). 
    Called 8 time(s). 
    Called 9 time(s). 
    Called 10 time(s). 
fib(3) = 3 
fib was called a total of 0 time(s). 

为什么在最后一行fib.__callcount等于0？如输出所示，__callcount得到递增，并在fib的调用之间持续存在。

我错过了什么？

Answer 1

好吧，这是原因，在一些帮助后。多谢你们！

问题是函数是不可变的。例如

>>> def f(func): 
...  return func() 
... 
>>> def g(): 
...  return 'sunflower seeds' 
... 
>>> id(g) 
139636515497336 
>>> g = f(g) 
>>> id(g) 
139636515515112 

因此，要获得功能f的唯一途径，我们分配__callcount属性中的countcalls的定义是从callcount返回功能。但是我们已经返回了内部函数_countcalls。我们可以返回f和_countcalls，但是这会弄乱@countcalls装饰器语法。

你仍然可以这样做，它只是不那么漂亮。

import functools 

def countcalls(f): 
    f.__callcount = 0 

    @functools.wraps(f) 
    def _countcalls(*args, **kwds): 
     f.__callcount += 1 
     print(' Called {0} time(s).'.format(f.__callcount)) 
     return f(*args, **kwds) 
    return f, _countcalls 

def fib(n): 
    if n < 0: 
     raise ValueError('n must be > 0') 
    if n == 0 or n == 1: 
     return 1 

    return fib(n-1) + fib(n-2) 

if __name__ == '__main__': 
    counter, fib = countcalls(fib) 

    print('Calling fib(3)...') 
    x = fib(3) 
    print('fib(3) = {0}'.format(x)) 

    print('Calling fib(3) again...') 
    x = fib(3) 
    print('fib(3) = {0}'.format(x)) 

    print('fib was called a total of {0} time(s).'.format(counter.__callcount)) 

长话短说，只是使用class from the Python Decorator Library。 ：D

Answer 2

f.__callcount = [0] 

.......... 


f.__callcount[0] = f.__callcount[0] + 1 

...... 


print('fib was called a total of {0} time(s).'.format(fib.__callcount[0])) 

它的工作原理。
也许它的东西更pythonic

Answer 3

这就是你想要的。我知道了这里 - https://wiki.python.org/moin/PythonDecoratorLibrary#Alternate_Counting_function_calls

class countcalls(object): 
    "Decorator that keeps track of the number of times a function is called." 

    __instances = {} 

    def __init__(self, f): 
     self.__f = f 
     self.__numcalls = 0 
     countcalls.__instances[f] = self 
     self.__doc__ = f.func_doc 
     self.__name__ = f.func.func_name 

    def __call__(self, *args, **kwargs): 
     self.__numcalls += 1 
     return self.__f(*args, **kwargs) 

    def count(self): 
     "Return the number of times the function f was called." 
     return countcalls.__instances[self.__f].__numcalls 

    @staticmethod 
    def counts(): 
     "Return a dict of {function: # of calls} for all registered functions." 
     return dict([(f.__name__, countcalls.__instances[f].__numcalls) for f in countcalls.__instances]) 

@countcalls 
def fib(n): 
    if n < 0: 
     raise ValueError('n must be > 0') 
    if n == 0 or n == 1: 
     return 1 

    return fib(n-1) + fib(n-2) 

if __name__ == '__main__': 
    print('Calling fib(3)...') 
    x = fib(3) 
    print('fib(3) = {0}'.format(x)) 
    print('fib was called a total of {0} time(s).'.format(fib.count())) 

    print('Calling fib(3) again...') 
    x = fib(3) 
    print('fib(3) = {0}'.format(x)) 

    print('fib was called a total of {0} time(s).'.format(fib.count())) 

Answer 4

的函数对象要添加的属性是不同的对象比“原始”功能。试试这个：

import functools 

def countcalls(f): 
    f.__callcount = 0 

    @functools.wraps(f) 
    def _countcalls(*args, **kwds): 
     f.__callcount += 1 
     print 'id(f):', id(f) 
     print(' Called {0} time(s).'.format(f.__callcount)) 
     return f(*args, **kwds) 
    return _countcalls 


@countcalls 
def fib(n): 
    """fibinacci""" 
    if n < 0: 
     raise ValueError('n must be > 0') 
    if n == 0 or n == 1: 
     return 1 

    return fib(n-1) + fib(n-2) 


if __name__ == '__main__': 
    print('Calling fib(3)...') 
    x = fib(3) 
    print 'id(fib):', id(fib) 

""" 
>>> 
Calling fib(3)... 
id(f): 45611952 
    Called 1 time(s). 
id(f): 45611952 
    Called 2 time(s). 
id(f): 45611952 
    Called 3 time(s). 
id(f): 45611952 
    Called 4 time(s). 
id(f): 45611952 
    Called 5 time(s). 
id(fib): 45612016 
>>> 
"""