deque in python

>>> from collections import deque
>>> d = deque('ghi')          # make a new deque with three items
>>> for elem in d:            # iterate over the deque's elements
...     print elem.upper()
G
H
I

>>> d.append('j')             # add a new entry to the right side
>>> d.appendleft('f')         # add a new entry to the left side
>>> d                         # show the representation of the deque
deque(['f', 'g', 'h', 'i', 'j'])

>>> d.pop()                   # return and remove the rightmost item
'j'
>>> d.popleft()               # return and remove the leftmost item
'f'
>>> list(d)                   # list the contents of the deque
['g', 'h', 'i']
>>> d[0]                      # peek at leftmost item
'g'
>>> d[-1]                     # peek at rightmost item
'i'

>>> list(reversed(d))         # list the contents of a deque in reverse
['i', 'h', 'g']
>>> 'h' in d                  # search the deque
True
>>> d.extend('jkl')           # add multiple elements at once
>>> d
deque(['g', 'h', 'i', 'j', 'k', 'l'])
>>> d.rotate(1)               # right rotation
>>> d
deque(['l', 'g', 'h', 'i', 'j', 'k'])
>>> d.rotate(-1)              # left rotation
>>> d
deque(['g', 'h', 'i', 'j', 'k', 'l'])

>>> deque(reversed(d))        # make a new deque in reverse order
deque(['l', 'k', 'j', 'i', 'h', 'g'])
>>> d.clear()                 # empty the deque
>>> d.pop()                   # cannot pop from an empty deque
Traceback (most recent call last):
  File "<pyshell#6>", line 1, in -toplevel-
    d.pop()
IndexError: pop from an empty deque

>>> d.extendleft('abc')      # extendleft() reverses the input order
>>> d
deque(['c', 'b', 'a'])

# It is usefull when dealing with treads
from collections import deque
students = deque(('Sarah', 'Mary', 'Carl'))
students.append('Charlotte')                   # this name appear at the end of the deque
students.appendleft('Ruth')                    # this name appear at the start of the deque
students.pop()                                 # remove the element from the end
students.popleft()                             # remove the element from the start 
print(students)    

# Python code to demonstrate working of  
# append(), appendleft(), pop(), and popleft() 
  
# importing "collections" for deque operations 
import collections 
  
# initializing deque 
de = collections.deque([1,2,3]) 
  
# using append() to insert element at right end  
# inserts 4 at the end of deque 
de.append(4) 
  
# printing modified deque 
print ("The deque after appending at right is : ") 
print (de) 
  
# using appendleft() to insert element at right end  
# inserts 6 at the beginning of deque 
de.appendleft(6) 
  
# printing modified deque 
print ("The deque after appending at left is : ") 
print (de) 
  
# using pop() to delete element from right end  
# deletes 4 from the right end of deque 
de.pop() 
  
# printing modified deque 
print ("The deque after deleting from right is : ") 
print (de) 
  
# using popleft() to delete element from left end  
# deletes 6 from the left end of deque 
de.popleft() 
  
# printing modified deque 
print ("The deque after deleting from left is : ") 
print (de)