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

from collections import defaultdict
list1 = [("id1","host1"),("id2","host2"),("id1","host5"),("id3","host4"),("id4","host6"),("id5","host8")]
list2 = [("id1","IP1"),("id2","IP2"),("id3","IP3"),("id4","IP4"),("id5","IP5")]
host = defaultdict(list)
IP4id = {}
for k, v in list2:
    IP4id[v] = {"id" : k, "host" : []}

for k, v in list1:
    host[k].append(v)

for item in IP4id:
    IP4id[item]["host"] = host[IP4id[item]["id"]]
print IP4id