[PEAK] Peak rules example's simplification

[Alexander Artemenko]

Good day,

>> I found, that  example at http://pypi.python.org/pypi/PEAK-Rules/ page
>> can be simplified by omiting one part of the predicate in
>> pprint_long_list:
>>
>> # Skip Skip
>> >>> @when(pprint, (list,))
>> ... def pprint_list(lst):
>> ...     print "pretty-printing a list"
>>
>> >>> @when(pprint_list, "len(lst)>50") # Change 'pprint' to 'pprint_list'
>> >>> here and remove type check
>> ... def pprint_long_list(lst):
>> ...     print "pretty-printing a long list"
>>
>> # Skip Skip
>>
>> Is it feature or bug?
>> Which are the best practices in function extention, using Peak.Rules?
>
> Your version is still correct, but potentially much slower, since it does
> dispatching *twice*...  once to invoke pprint_list, and then once to select
> whether to run the original pprint_list or pprint_long_list.  This is slower
> because the dispatch algorithm runs more than once, and because the
> dispatcher can't optimize complex conditions that are split between the two
> functions.
>
> The only benefit to the way you're doing it here is that if pprint_list is
> ever used independently, it will still be modified by pprint_long_list.  But
> I'm not sure that even that is really a "benefit".

You right, but how about DRY priciple? My variant allows to not repeat one
predicate - 'isinstance(obj, (list,))'. Wat if later I'll decide to
change it, to accept
tuples or even iterators?

Is there any way to not repeat predicates from previous methods? Something like
decorators inheritance?

Thanks,
-- 
Alexander Artemenko (a.k.a. Svetlyak 40wt)
Blog: http://aartemenko.com
Photos: http://svetlyak.ru
Jabber: svetlyak.40wt at gmail.com