On 9/28/14 8:04 PM, David Alban wrote:
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?
If you want file_data to be a dictionary of dictionaries, use a defaultdict:
file_data = collections.defaultdict(dict)
This is Python's version of autovivification. When you access a key
that doesn't exist, the defaultdict will use the callable you gave it
(in this case, dict) to create the new value as needed.
--
Ned Batchelder, http://nedbatchelder.com
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