python defaultdict: 0 vs. int and [] vs list
collections, defaultdict, python
Solution
All that `defaultdict` requires is a callable object that will return what should be used as a default value when called with no parameters.
If you were to call the `int` constructor, it would return `0` and if you were to call `lambda: 0`, it would return `0`. Same with the lists. The only difference here is that the constructor will always use it's logic to create the object. A lambda, you could add additional logic if you chose to do so.
e.g.,
# alternating between `0` and `[]`
from itertools import count
factory = lambda c=count(): 0 if next(c) % 2 else []
superdict = defaultdict(factory)
Problem
Is there any difference between passing `int` and `lambda: 0` as arguments? Or between `list` and `lambda: []`? It looks like they do the same thing: ``` from collections import defaultdict dint1 = defaultdict(lambda: 0) dint2 = defaultdict(int) dlist1 = defaultdict(lambda: []) dlist2 = defaultdict(list) for ch in 'abracadabra': dint1[ch] += 1 dint2[ch] += 1 dlist1[ch].append(1) dlist2[ch].append(1) print dint1.items() print dint2.items() print dlist1.items() print dlist2.items() ## -- Output: -- [('a', 5), ('r', 2), ('b', 2), ('c', 1), ('d', 1)] [('a', 5), ('r', 2), ('b', 2), ('c', 1), ('d', 1)] [('a', [1, 1, 1, 1, 1]), ('r', [1, 1]), ('b', [1, 1]), ('c', [1]), ('d', [1])] [('a', [1, 1, 1, 1, 1]), ('r', [1, 1]), ('b', [1, 1]), ('c', [1]), ('d', [1])] ``` but are there any cases where they'll have different behavior, or is it merely a notational difference?