collections.defaultdict()
collections.defaultdict() is a Python function in the Collections Module category. A dict subclass that calls a factory function to supply missing values. The syntax is collections.defaultdict(default_factory). Parameters: default_factory — callable for default values. Returns: DefaultDict object. A typical example: from collections import defaultdict
d = defaultdict(list)
d["x"].append(1) # No KeyError!. A close sibling is collections.deque(), which returns a double-ended queue (deque) with efficient O(1) appends/pops from both ends. A close sibling is deque.append(), which adds x to the right side of the deque. A close sibling is deque.appendleft(), which adds x to the left side of the deque. A close sibling is deque.pop(), which removes and returns the rightmost element. Raises IndexError if empty. More about this category: Specialized container datatypes — deque, Counter, defaultdict, namedtuple, OrderedDict. For a broader walkthrough, read the Collections Module guide. Related Collections Module entries: collections.deque(), deque.append(), deque.appendleft(), deque.pop(), deque.popleft(), deque.extend().