Python merge lists by common element

Question

Im trying to merge two lists that have a common thing between them (in that case is a the id parameter). I have something like this:

list1=[(id1,host1

Answer 1

1. use collections.defaultdict to map id->ip
2. then map id -> ip

>>> d = defaultdict(set)
>>> d['id'].add('host1')
>>> d['id'].add('host2')
>>> d['id'].add('host1')
>>> d
defaultdict(, {'id': set(['host2', 'host1'])})