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Python – Decrement Dictionary value by K

  • Last Updated : 17 Dec, 2019
Geek Week

Sometimes, while working with dictionaries, we can have a use-case in which we require to decrement a particular key’s value by K in dictionary. It may seem a quite straight forward problem, but catch comes when the existence of a key is not known, hence becomes a 2 step process at times. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using get()
The get function can be used to initialize a non-existing key with 0 and then the decrement is possible. By this way the problem of non-existing key can be avoided.




# Python3 code to demonstrate working of
# Decrement Dictionary value by K
# Using get()
  
# Initialize dictionary
test_dict = {'gfg' : 1, 'is' : 2, 'for' : 4, 'CS' : 5}
  
# printing original dictionary
print("The original dictionary : " + str(test_dict))
  
# Initialize K 
K = 5
  
# Using get()
# Decrement Dictionary value by K
test_dict['best'] = test_dict.get('best', 0) - K
      
# printing result 
print("Dictionary after the decrement of key : " + str(test_dict))
Output :

The original dictionary : {‘for’: 4, ‘CS’: 5, ‘is’: 2, ‘gfg’: 1}
Dictionary after the decrement of key : {‘best’: -5, ‘for’: 4, ‘CS’: 5, ‘is’: 2, ‘gfg’: 1}

 



Method #2 : Using defaultdict()
This problem can also be solved by using a defaultdict method, which initializes the potential keys and doesn’t throw an exception in case of non-existence of keys.




# Python3 code to demonstrate working of
# Decrement Dictionary value by K
# Using defaultdict()
from collections import defaultdict
  
# Initialize dictionary
test_dict = defaultdict(int)
  
# printing original dictionary
print("The original dictionary : " + str(dict(test_dict)))
  
# Initialize K 
K = 5
  
# Using defaultdict()
# Decrement Dictionary value by K
test_dict['best'] -= K
      
# printing result 
print("Dictionary after the decrement of key : " + str(dict(test_dict)))
Output :

The original dictionary : {}
Dictionary after the decrement of key : {‘best’: -5}

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