>> Over lunch with Alex Martelli, he proposed that a subclass of dict
>> with this behavior (but implemented in C) would be a good addition to
>> the language
I would like to add something like this to the collections module, but a PEP is
probably needed to deal with issues like:
* implications of a __getitem__ succeeding while get(value, x) returns x
(possibly different from the overall default)
* implications of a __getitem__ succeeding while __contains__ would fail
* whether to add this to the collections module (I would say yes)
* whether to allow default functions as well as default values (so you could
instantiate a new default list)
* comparing all the existing recipes and third-party modules that have already
done this
* evaluating its fitness for common use cases (i.e. bags and dict of lists).
* lay out a few examples:
# bag like behavior
dd = collections.default_dict()
dd.default(0)
for elem in collection:
dd[elem] += 1
# setdefault-like behavior
dd = collections.default_dict()
dd.default(list) # instantiate a new list for
empty cells
for page_number, page in enumerate(book):
for word in page.split():
dd[word].append(word)
Raymond
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