Pre-PEP: Dictionary accumulator methods

[Kent Johnson]

Bengt Richter wrote:
> On Sat, 19 Mar 2005 01:24:57 GMT, "Raymond Hettinger" <vze4rx4y at verizon.net> wrote:
> 
>>I would like to get everyone's thoughts on two new dictionary methods:
>>
>>       def count(self, value, qty=1):
>>           try:
>>               self[key] += qty
>>           except KeyError:
>>               self[key] = qty
>>
>>       def appendlist(self, key, *values):
>>           try:
>>               self[key].extend(values)
>>           except KeyError:
>>               self[key] = list(values)
>>
> How about an efficient duck-typing value-incrementer to replace both? E.g. functionally like:
> 
>  >>> class xdict(dict):
>  ...     def valadd(self, key, incr=1):
>  ...         try: self[key] = self[key] + type(self[key])(incr)
>  ...         except KeyError: self[key] = incr

A big problem with this is that there are reasonable use cases for both
   d.count(key, <some integer>)
and
   d.appendlist(key, <some integer>)

Word counting is an obvious use for the first. Consolidating a list of key, value pairs where the 
values are ints requires the second.

Combining count() and appendlist() into one function eliminates the second possibility.

Kent