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From: Peter Otten <__peter__@web.de>
Newsgroups: comp.lang.python
Subject: Re: subclassing collections.Counter
Date: Tue, 15 Dec 2015 17:08:15 +0100
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Xref: csiph.com comp.lang.python:100467

Pavlos Parissis wrote:

> I need to store values for metrics and return the average for some
> and the sum for the rest. Thus, I thought I could extend
> collections.Counter class by returning averages for some keys.
> 
> My class modifies the update() to increment a counter and the
> __getitem__ to perform the calculation. But, I get RuntimeError: maximum
> recursion depth exceeded as I access an attribute inside
> __getitem__.
> 
> Does anyone has an idea how I can achieve this?

> class CounterExt(Counter):

>     def __getitem__(self, key):
>         if (self.avg_metrics is not None and key in self.avg_metrics):
>             return self[key] / self._counter
>         else:
>             return self[key]

self[key] will call the CounterExt.__getitem__() method again. Use 
super().__getitem__(key) instead to invoke Counter.__getitem__().