Python decorator that checks if function was called before
<p>I need to make a decorator that checks if the function that its associated with was called before with exactly the same arguments as its being called with now.  If it was, I need to return the previous output.  If not I call it and store the result for future calls. Here is what I have:</p>

<pre><code>class memoized(object):
    def __init__(self,f):
        self.__first=[]
        self.__last=[]
        self.__f=f
        self.__name__=f.__name__
        self.__value=[]
    def __call__(self,*args,**dargs):
        for i in self.__value:
            if(self.__first[i]==args and self.__last[i]==dargs):
                return self.__value[i]
        rv=self.__f(*args,**dargs)
        self.__first.append(args)
        self.__last.append(dargs)
        self.__value.append(rv)
        return rv
</code></pre>

<p>when I run it though it gives me an idex error. Im not sure why since theoretically the length of value first and last should be the same all the time because I append to all 3 of them.  Any ideas?</p>