Questions tagged [defaultdict]

This tag would be applicable to Python questions related with the instantiation, filling and subclassing of the collections.defaultdict class.

defaultdict is a subclass of the built-in dict class. It overrides one method and adds one writable instance variable. The remaining functionality is the same as for the dict class.

collections.defaultdict([default_factory[, ...]])

The first argument provides the initial value for the default_factory attribute; it defaults to None. Commonly used default_factories are int, list or dict.

>>> s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
>>> d = defaultdict(list)
>>> for k, v in s:
...     d[k].append(v)
...
>>> d.items()
[('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])]

this is equivalent to:

>>> d = dict()
>>> for k, v in s:
...     d.setdefault(k, []).append(v)
...

http://docs.python.org/library/collections.html