library collections python code example

Example 1: python collections

# Dictionary where key values default to a list:
	a = collections.defaultdict(list)   
# Dictionary where key values default to 0:
	a = collections.defaultdict(int)
# Dictionary where key values default to another dictionary:
	a = collections.defaultdict(dict)

'''
Example:
  In a regular dictionary, if you did the following:
  
    a = {}
    if a['apple'] == 1:
        return True    
    else:
        return False
        
  You'd get an error, because 'apple' does not exist in dictionary. 
  However, if you use collections:
    
    a = collections.defaultdict(int)
    if a['apple'] == 1:
		return True
    else:
        return False
    
  This would not give an error, and False would be returned.
  Also, the dictionary would now have the key 'apple' with a
  default integer value of 0 inside it.
  
  If you used say, collections.defaultdict(list), the default value
  would be an empty list instead of 0.
  
'''

Example 2: python collections

list = [1,2,3,4,1,2,6,7,3,8,1]
Counter(list)