[Tutor] Counting method calls

[Daniel Kavic]

Ok I have been a multimedia major for a few years now. I have tried  
javascript and that was bad, Java is just too difficult, so I joined  
this mailing list a while back. I have been frustrated because I just  
don't get entirely how OOProgramming works and how to actually write  
the stuff correctly. I have a hard time programming and I wish I  
could be better at knowing at least one language. I need a really  
good book or something to explain this to me. I am not the best in math
On Sep 22, 2007, at 12:46 PM, Kent Johnson wrote:

> Ricardo Aráoz wrote:
>> Kent Johnson wrote:
>
>>> What version of Python are you using? When I try this program it  
>>> prints
>>
>> Py 0.9.5
>> Python 2.5 (r25:51908, Sep 19 2006, 09:52:17) [MSC v.1310 32 bit
>> (Intel)] on win32
>>
>> I thought it might be you were trying the class with the list init  
>> call
>> but I tried it and works the same way.
>> Was using PyAlaMode, tried it using IDLE and it works like yours,
>> probably a bug of PyAlaMode.
>
> My guess is PyAlaMode is trying to introspect the objects in some way
> and that is causing the extra access (to non-existent attributes).
>
>>> class CallCounter(object):
>>>      def __init__(self, delegate):
>>>          self._delegate = delegate
>>>          self.calls = 0
>>>      def __getattr__(self, name):
>>>          value = getattr(self._delegate, name)
>>>          if callable(value):
>>>              self.calls += 1
>>>          return value
>>>
>>> a = CallCounter(list())
>>
>> Sadly :
>>>>> a = CallCounter(list())
>>>>> a.append(1)
>>>>> a.calls
>> 2
>>>>> a.append(2)
>>>>> a.append(3)
>>>>> a.calls
>> 5
>>>>> a[3]
>>
>> Traceback (most recent call last):
>>   File "<pyshell#15>", line 1, in <module>
>>     a[3]
>> TypeError: 'CallCounter' object is unindexable
>
> Hmm. The problem is that new-style classes don't look up special  
> methods
> on instances, just in the class itself.
>
> There is some discussion here, it looks a bit ugly:
> http://groups.google.com/group/comp.lang.python/browse_thread/ 
> thread/c5bb6496970b5c5a?hl=en&tvc=2
> Alex Martelli's second response proposes a solution that overrides
> __new__() to create a custom class for each wrapper.
>
> There might be some help here too, I haven't read it closely:
> http://tinyurl.com/25lx5t
>
> The code works if CallCounter is an old-style class.
>
> Kent
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