import collections
d = collections.deque([])
print('d = {}'.format(d))
d.appendleft(4)
print('d = {}'.format(d))
d.append(2)
print('d = {}'.format(d))
cardinality = len(d)
print('cardinality = {}'.format(cardinality))
head = d[0]
print('head = {}'.format(head))
tail = d[-1]
print('tail = {}'.format(tail))
popped_head = d.popleft()
print('popped_head = {}'.format(popped_head))
print('d = {}'.format(d))
popped_tail = d.pop()
print('popped_tail = {}'.format(popped_tail))
print('d = {}'.format(d))