a double-ended queue, or deque, supports adding and removing elements from either end of the queue

a mutable, sequential data structure

from collections import deque

a = deque('abcdefg') #deque(['a', 'b', 'c', 'd', 'e', 'f', 'g'])
print(a)
b = deque(['Hello', 2]) # deque(['Hello', 2])
print(len(b))
			

print(a[0]) # a
a[0] = 'h' # deque(['h', 'b', 'c', 'd', 'e', 'f', 'g'])
            

d = deque('abcdefg')

# append, add a new entry to the right side
d.append('j') # deque(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'j'])

# appendleft, add a new entry to the left side
d.appendleft('f') # deque(['f', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'j'])

# pop
print(d.pop()) # j, return and remove the rightmost item

# popleft
print(d.popleft()) # f, return and remove the leftmost item

print(d) # deque(['a', 'b', 'c', 'd', 'e', 'f', 'g'])
print(d[0]) # a, peek at leftmost item
print(d[-1]) # g, peek at rightmost item

# extend, add multiple elements at once
d.extend(['Hello', 'World']) # deque(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'Hello', 'World'])

# rotate
d.rotate(3) # deque(['g', 'Hello', 'World', 'a', 'b', 'c', 'd', 'e', 'f']), right rotation
d.rotate(-2) # deque(['World', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'Hello']), left rotation

# clear, empty the deque
d.clear()
            

b = deque(['Hello', 2]) # deque(['Hello', 2])
print(len(b)) # 2

l = list(b) # ['Hello', 2]
print(l)

list(reversed(b)) # [2, 'Hello']

b = deque(reversed(b)) # deque([2, 'Hello']), make a new deque in reverse order
print(b)
            

Python 3 Standard Library

Python 3 Module of the Week