dequeue python code example

Example 1: deque 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'])

Example 2: python counter

sum(c.values())                 # total of all counts
c.clear()                       # reset all counts
list(c)                         # list unique elements
set(c)                          # convert to a set
dict(c)                         # convert to a regular dictionary
c.items()                       # convert to a list of (elem, cnt) pairs
Counter(dict(list_of_pairs))    # convert from a list of (elem, cnt) pairs
c.most_common()[:-n-1:-1]       # n least common elements
c += Counter()                  # remove zero and negative counts

Example 3: python counter

>>> c = Counter(a=4, b=2, c=0, d=-2)
>>> d = Counter(a=1, b=2, c=3, d=4)
>>> c.subtract(d)
>>> c
Counter({'a': 3, 'b': 0, 'c': -3, 'd': -6})