[Baypiggies] Notes on defaultdict

[Chris Clark]

Great discussion, thanks for kicking this off Glen!

As Brian pointed out syntax/simplicity is the reason for default dict, 
performance is not in the running. I actually almost never use the 
defaultdict, part of the reason is that I'm often on a pre 2.5 
interpreter. You can use the regular dict and still keep the code fairly 
clean using get(), but it isn't as nice as defaultdict.

"""Performance figures/output from my desktop:

12.9385441449 def_dict
6.60369553361 reg_dict

"""
import timeit

def def_dict():
    from collections import defaultdict  # NOTE needs python 2.5+

    input = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), 
('red', 1)]

    output = defaultdict(list)
    for color, value in input:
        output[color].append(value)

def reg_dict():
    input = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), 
('red', 1)]

    output2 = {}
    for color, value in input:
        tmp_entry = output2.get(color, [])
        tmp_entry.append(value)
        output2[color] = tmp_entry

if __name__ == '__main__':
    names = ['def_dict', 'reg_dict']
    m = 5
    m = 1000000
    for name in names:
        t = timeit.Timer('%s()' % name, 'from __main__ import %s' % name)
        tmp_time = t.timeit(m)
        print tmp_time, name

NOTE I followed Brian's approach of timing the import from collections, 
and setting up the source list.

Chris



Glen Jarvis wrote:
>
>     Great notes -- thanks for posting them, I'm glad to see them as I
>     wasn't able to be at the meeting.
>
>     Did you mention the __missing__ magic method, in Python 2.5 and up,
>     which can be used for defaultdict-like (and other fun) behavior?
>
>
> I didn't... I didn't know about it, actually... In the future, I 
> obviously need to send this *first* to BayPIGgies a few weeks ahead to 
> get all of this valuable feedback up front. There are still layers to 
> learn/understand here. We have *plenty* of choices to handle this one 
> itty bitty situation... 
>
> Cheers,
>
>
> Glen
> -- 
> Whatever you can do or imagine, begin it;
> boldness has beauty, magic, and power in it.
>
> -- Goethe
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