David Alban wrote:
> greetings,
>
> i'm writing a program to scan a data file. from each line of the data
> file
> i'd like to add something like below to a dictionary. my perl background
> makes me want python to autovivify, but when i do:
>
> file_data = {}
>
> [... as i loop through lines in the file ...]
>
> file_data[ md5sum ][ inode ] = { 'path' : path, 'size' : size, }
>
> i get:
>
> Traceback (most recent call last):
> File "foo.py", line 45, in <module>
> file_data[ md5sum ][ inode ] = { 'path' : path, 'size' : size, }
> KeyError: '91b152ce64af8af91dfe275575a20489'
>
> what is the pythonic way to build my "file_data" data structure above that
> has the above structure?
Others have suggested using a defaultdict, but here's an older solution: use
the setdefault method on regular dicts.
This fails:
py> file_data = {}
py> file_data[1234][23] = {'spam': 1, 'eggs': 2}
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
KeyError: 1234
But this succeeds:
py> file_data.setdefault(1234, {})[23] = {'spam': 1, 'eggs': 2}
py> file_data.setdefault(5678, {})[42] = {'spam': 3, 'cheese': 1}
py> file_data
{1234: {23: {'spam': 1, 'eggs': 2}}, 5678: {42: {'spam': 3, 'cheese': 1}}}
Whether you prefer to use setdefault, or a defaultdict, is a matter of
taste.
--
Steven
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