deque python

from collections import defaultdict 
  
# Defining a dict containing lists 
d = defaultdict(list) 
  
for i in range(5): 
    d[i].append(i) 
      
print("Dictionary with values as list:") 
print(d) 

#Output:
#Dictionary with values as list:
#defaultdict(<class 'list'>, {0: [0], 1: [1], 2: [2], 3: [3], 4: [4]})

from collections import OrderedDict 
od = OrderedDict()

An OrderedDict is a dictionary subclass that remembers the order 
that keys were first inserted. A regular dict doesn’t track the 
insertion order, and iterating it gives the values in an arbitrary 
order.
# A Python program to demonstrate working of OrderedDict 
from collections import OrderedDict 
d = {} # regular dict
d['a'] = 1
d['b'] = 2
d['c'] = 3
for key, value in d.items(): 
    print(key, value) 
# Output
# ('a', 1)
# ('c', 3)
# ('b', 2)  
od = OrderedDict() # Ordered Dict
od['a'] = 1
od['b'] = 2
od['c'] = 3
for key, value in od.items(): 
    print(key, value) 
# Output
# ('a', 1)
# ('b', 2)
# ('c', 3)

>>> # regular unsorted dictionary
>>> d = {'banana': 3, 'apple': 4, 'pear': 1, 'orange': 2}

>>> # dictionary sorted by key
>>> OrderedDict(sorted(d.items(), key=lambda t: t[0]))
OrderedDict([('apple', 4), ('banana', 3), ('orange', 2), ('pear', 1)])

>>> # dictionary sorted by value
>>> OrderedDict(sorted(d.items(), key=lambda t: t[1]))
OrderedDict([('pear', 1), ('orange', 2), ('banana', 3), ('apple', 4)])

>>> # dictionary sorted by length of the key string
>>> OrderedDict(sorted(d.items(), key=lambda t: len(t[0])))
OrderedDict([('pear', 1), ('apple', 4), ('orange', 2), ('banana', 3)])

>>> 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)    

most_common([n])¶
Return a list of the n most common elements and their counts from the most common to the least. If n is omitted or None, most_common() returns all elements in the counter.
Elements with equal counts are ordered arbitrarily:

>>> Counter('abracadabra').most_common(3)
[('a', 5), ('r', 2), ('b', 2)]

>>> Counter('abracadabra').most_common(3)
[('a', 5), ('r', 2), ('b', 2)]

>>> # Tally occurrences of words in a list
>>> cnt = Counter()
>>> for word in ['red', 'blue', 'red', 'green', 'blue', 'blue']:
...     cnt[word] += 1
>>> cnt
Counter({'blue': 3, 'red': 2, 'green': 1})

>>> # Find the ten most common words in Hamlet
>>> import re
>>> words = re.findall(r'\w+', open('hamlet.txt').read().lower())
>>> Counter(words).most_common(10)
[('the', 1143), ('and', 966), ('to', 762), ('of', 669), ('i', 631),
 ('you', 554),  ('a', 546), ('my', 514), ('hamlet', 471), ('in', 451)]

# 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)