How to make lists automatically instantiate on use in Python as they do in Perl? -

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in perl, can this:

push(@{$h->[x]}, y);

can simplify following python codes according above perl example?

if x not in h:   h[x] = [] h[x].append(y)

i want simplify this, because goes many places in code, (and cannot initialize possible x []). not want make function, because there no 'inline' keyword.

any ideas?

a elegant way (since python 2.5) use defaultdict "collections" module:

>>> collections import defaultdict >>> h = defaultdict(list) >>> h['a'].append('b') >>> h defaultdict(<type 'list'>, {'a': ['b']})

defaultdict dict, provides default value using whichever constructor passed when created (in example, list).

i particularly on setdefault dict method, because 1) define variable defaultdict, , no other changes required on code (except perhaps remove previous kludges default values); , 2) setdefault terrible name :p


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