在Python中为每个实例装饰方法 [英] Decorate methods per instance in Python

问题描述

假设我有一些简单的课程

Assume I have some simple class

class TestClass:
    def doSomething(self):
        print 'Did something'

我想装饰 doSomething 方法，例如计算呼叫次数

I would like to decorate the doSomething method, for example to count the number of calls

class SimpleDecorator(object):
    def __init__(self,func):
        self.func=func
        self.count=0
    def __get__(self,obj,objtype=None):
        return MethodType(self,obj,objtype)
    def __call__(self,*args,**kwargs):
        self.count+=1
        return self.func(*args,**kwargs)

现在，这计算了对装饰方法的调用次数，但是我希望每个实例都有一个计数器，例如

Now this counts the number of calls to the decorated method, however I would like to have per-instance counter, such that after

foo1=TestClass()
foo1.doSomething()
foo2=TestClass()

foo1.doSomething.count 为1和 foo2.doSomething.count 为0。据我了解，使用装饰器是不可能的。有什么方法可以实现这种行为？

foo1.doSomething.count is 1 and foo2.doSomething.count is 0. From what I understand, this is not possible using decorators. Is there some way to achieve such behaviour?

推荐答案

利用自己（即调用该方法的对象）作为参数传递给该方法：

Utilize the fact that self (i.e. the object which the method is invoked on) is passed as a parameter to the method:

import functools

def counted(method):
    @functools.wraps(method)
    def wrapped(obj, *args, **kwargs):
        if hasattr(obj, 'count'): 
            obj.count += 1
        else:
            obj.count = 1
        return method(obj, *args, **kwargs)
    return wrapped

在上面的代码中，我们将对象拦截为 obj 方法的修饰版本的参数。装饰器的用法非常简单：

In above code, we intercept the object as obj parameter of the decorated version of method. Usage of the decorator is pretty straightforward:

class Foo(object):
    @counted
    def do_something(self): pass

这篇关于在Python中为每个实例装饰方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！