defaultdict use

gistfile1.py

# instead of this
x, y, z = 1, 2, 3
d = {}
if not d.has_key(x):
  d[x] = {}
if not d[x].has_key(y):
  d[x][y] = []
d[x][y].append(z)

# this
from collections import defaultdict
d = defaultdict(lambda : defaultdict(list))
d[x][y].append(z)

x, y, z = 1, 2, 3                                                               
d = {}                                                                          
t = d.setdefault(x, {}).setdefault(y, [])                                       
t[x][y] = z