Python

collections:

counter class

• Count uniq element from given list. Result is return in the format of tuple. Example:

   from collections import Counter
   my_list = [1,1,1,2,2,2,2,3,3,3,3,3]
   Counter(my_list)
   str_var = 'Bhushan Patil'
   Counter(str_var)
   statement = 'India is my country and I live in Maharashtra state of India. My Home is in Pune'
   Counter(statement.split())
  

  Output:

   Counter({1: 3, 2: 4, 3: 5})
   Counter({'B': 1,
       'h': 2,
       'u': 1,
       's': 1,
       'a': 2,
       'n': 1,
       ' ': 1,
       'P': 1,
       't': 1,
       'i': 1,
       'l': 1})
   Counter({'India': 1,
       'is': 2,
       'my': 1,
       'country': 1,
       'and': 1,
       'I': 1,
       'live': 1,
       'in': 2,
       'Maharashtra': 1,
       'state': 1,
       'of': 1,
       'India.': 1,
       'My': 1,
       'Home': 1,
       'Pune': 1})
  

Important method from counter class

method name	description
sum(counter_var.values())	summation of all values from counter
counter_var.clear	reset all counts
list(counter_var)	convert counter class instance into list
set(counter_var)	convert counter class instance into set
dict(counter_var)	convert counter class instance into dict
counter_var.items()	convert counter class instance key-value pair
counter_var.most_common()[:n-1:-1]	n least common elements
counter_var += counter()	remove zero and negative counts from result.

Differences between defaultdict & dict

• When we create dict object with defaultdict class all unavailable key will not throw an error at the time of retriving them. Example of creating dictionary from dict -

   dict_var = {'a':1, 'b':2, 'c':3}
   print(dict_var['q'])
  

  Output -

   File "<ipython-input-1-50cdd1217da3>", line 2
       print(dict_var['a'])
       ^
   IndentationError: unexpected indent
  

  Example of creating dictionary from defaultdict class -

   from collections import defaultdict
   dict_var = defaultdict(lambda:0)
   print(dict_var)
   print(dict_var['new_key'])
   print(dict_var)
   dict_var['new_key']=65
   print(dict_var['new_key'])
   print(dict_var)
  

  Output -

   defaultdict(<function <lambda> at 0x0000020CFD4F33A0>, {})
   0
   defaultdict(<function <lambda> at 0x0000020CFD4F33A0>, {'new_key': 0})
   65
   defaultdict(<function <lambda> at 0x0000020CFD4F33A0>, {'new_key': 65})
  

Differences between tuple & namedtuple

• tuples are only accessible through index while namedtuple also accessible through name.
• In tuples, always need to remember index of elements. Example of accessing element from tuple -

   tuple_var = (10, 20, 30)
   print(tuple_var[1])
  

  Output -

   20
  

  Example of creating tuple from namedtuple class -

   from collections import namedtuple
   Dog = namedtuple('Dog',['age', 'name', 'bread'])
   tommy_dog = Dog(age=3, name='tommy', bread='Huskey')
   print('=======Dog Information=======')
   print(f'Name : {tommy_dog.name}')
   print(f'Bread : {tommy_dog.bread}')
   print(f'Age : {tommy_dog.age}')
  

  Output -

   =======Dog Information=======
   Name : tommy
   Bread : Huskey
   Age : 3
  

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