En Wed, 24 Dec 2008 05:16:36 -0200, <pyt...@bdurham.com> escribió:
I'm looking for suggestions on the best ('Pythonic') way to
determine the difference between 2 very large dictionaries
containing simple key/value pairs.
By difference, I mean a list of keys that are present in the
first dictionary, but not the second. And vice versa. And a list
of keys in common between the 2 dictionaries whose values are
different.
The 2 strategies I'm considering are:
1. Brute force: Iterate through first dictionary's keys and
determine which keys it has that are missing from the second
dictionary. If keys match, then verify that the 2 dictionaries
have identical values for the same key. Repeat this process for
the second dictionary.
2. Use sets: Create sets from each dictionary's list of keys and
use Python's set methods to generate a list of keys present in
one dictionary but not the other (for both dictionaries) as well
as a set of keys the 2 dictionaries have in common.
I cannot think of any advantage of the first approach - so I'd use sets.
k1 = set(dict1.iterkeys())
k2 = set(dict2.iterkeys())
k1 - k2 # keys in dict1 not in dict2
k2 - k1 # keys in dict2 not in dict1
k1 & k2 # keys in both
Using the set
of keys in common, compare values across dictionaries to
determine which keys have different values (can this last step be
done via a simple list comprehension?)
Yes; but isn't a dict comprehension more adequate?
[key: (dict1[key], dict2[key]) for key in common_keys if
dict1[key]!=dict2[key]}
(where common_keys=k1&k2 as above)
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
