[Python-3000] A request to keep dict.setdefault() in 3.0

[Phillip J. Eby]

At 07:59 PM 7/9/2007 +0100, tav wrote:
>>PEP 3100 suggests dict.setdefault() may be removed in Python 3, since
>>it is in principle no longer necessary (due to the new defaultdict type).
>>
>>However, there is another class of use cases which use setdefault for
>>its limited atomic properties - the initialization of non-mutated
>>data structures that are shared among threads.  (And defaultdict
>>cannot achieve the same thing.)
>
>+1
>
>setdefault's ability to return current value is also a very useful
>functionality and has saved writing:
>
>  if key not in dict:
>    value = <compute-value>
>    dict[key] = value
>
>with the simpler:
>
>  value = dict.setdefault(key, <compute-value>)
>
>Is there a better way to do the above without .setdefault?

Yes, in 2.5 there's collections.defaultdict.  Of course, that only 
works if there is a fixed mapping from keys to initial computed 
values for the entire dictionary for all time.  Oh, and if your code 
gets to create the dictionary.  :)