deque - double ended queue

https://docs.python.org/2/library/collections.html

class collections.deque([iterable[, maxlen]])

Deques are a generalization of stacks and queues (the name is pronounced “deck” and is short for “double-ended queue”). Deques support thread-safe, memory efficient appends and pops from either side of the deque with approximately the same O(1) performance in either direction.

create a new deque object:

deque([1])

or

start = deque()
start.append(1)

plenty of methods:

append(x), appendleft(x), pop(), popleft(), remove(value), extend(iterable), extendleft(iterable)

defaultdict

Returns a new dictionary-like object.defaultdictis a subclass of the built-indictclass.

>>> 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])]

Counter

A counter is a dict subclass for counting hashtable objects.

>>> c = Counter()
>>> c['cnt'] += 1
>>> c
Counter({'cnt': 1})
>>>