Adding modified methods from another class without subclassing

[Peter Otten]

John O'Hagan wrote:

> On Mon, 22 Aug 2011 11:32:18 +0200
> Peter Otten <__peter__ at web.de> wrote:
> 
>> John O'Hagan wrote:
>> 
>> > I have a class like this:
>> > 
>> > class MySeq():
>> >     def __init__(self, *seq, c=12):
>> >         self.__c = c
>> >         self.__pc = sorted(set([i % __c for i in seq]))
>> >         self.order = ([[self.__pc.index(i % __c), i // __c] for i in
>> >         seq])
>> >         #other calculated attributes
>> > 
>> >     @property
>> >     def pitches(self):
>> >         return [self.__pc[i[0]] + i[1] * self.__c for i in self.order]
>> > 
>> >     #other methods
>> 
>> That makes me dizzy. Are there any maxims in the Zen of Python that this
>> piece doesn't violate?
> 
> "Now is better than never"?
> 
> I know it looks crazy to take something apart and put it back together, as
> in this *simplified* *example*

emphasis mine ;)

> , but it does have a meaningful use: reducing a
> series of musical notes to a unique irreducible form "__pc", ("prime form"
> in pitch-class set theory), but keeping track of the actual current
> manifestation of that form via the writeable "order" attribute. That's why
> "pitches" must be called with each reference, because it may change,
> unlike "__pc", which can only change if the instance is reinitialised.
> 
> I am open to more elegant suggestions, of course. :)
> [...]

Dunno. Maybe you could inherit from collections.(Mutable)Sequence and 
somewhat reduce the number of methods you'd have to implement. 
Or you introduce a Pitch (Python) class that knows about its pitch class, 
and put that into a normal list:

>>> class Pitch(int):
...     @property
...     def pitch_class(self):
...             return self % 12
...     def __repr__(self):
...             return "Pitch(%s, pitch_class=%s)" % (self, 
self.pitch_class)
...
>>> map(Pitch, [1,0,42])
[Pitch(1, pitch_class=1), Pitch(0, pitch_class=0), Pitch(42, pitch_class=6)]