Combining Dictionaries Of Lists In Python

Question

I have a very large collection of (p, q) tuples that I would like to convert into a dictionary of lists where the first item in each tuple is a key that indexes a list that

Answer 1

collections.defaultdict works like this:

from collections import defaultdict
dic = defaultdict(list)
for i, j in tuples:
    dic[i].append(j)

similar for the dicts:

a, b = {1:[2, 3], 2:[3]}, {1:[4], 3:[1]}
de = defaultdict(list, a)
for i, j in b.items():
    de[i].extend(j)