default_dict.py

# -*- coding: utf-8 -*-

from collections import defaultdict


src = [('a',1),('b',2),('c',3),('a',3)]

# 使わないとき

d = defaultdict(list)

result = {}

for i,j in src:
    if i in result:
        result[i].append(j)
    else:
        result[i] = [j]

print result

# defaultdict
for i,j in src:
    d[i].append(j)

print d