Python | Even values update in dictionary

Last Updated : 23 Jan, 2020

Sometimes, while working with dictionaries, we might come across a problem in which we require to perform a particular operation on even value of keys. This type of problem can occur in web development domain. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using loop
This is the naive method in which this task can be performed. In this we simply run a loop to traverse each key and check for even in dictionary and perform the desired operation.

# Python3 code to demonstrate working of
# Even values update in dictionary
# Using loop
  
# Initialize dictionary
test_dict = {'gfg' : 6, 'is' : 4, 'best' : 7}
  
# printing original dictionary
print("The original dictionary : " + str(test_dict))
  
# Using loop
# Even values update in dictionary
for key in test_dict: 
    if test_dict[key] % 2 == 0:
        test_dict[key] *= 3
  
# printing result 
print("The dictionary after triple even key's value : " + str(test_dict))

Output :

The original dictionary : {'best': 7, 'is': 4, 'gfg': 6}
The dictionary after triple even key's value : {'best': 7, 'is': 12, 'gfg': 18}

Method #2 : Using update() + dictionary comprehension
An alternate one-liner to perform this task, the combination of above functions can be used to perform this particular task. The update function is used to perform the necessary operation over the dictionary.

# Python3 code to demonstrate working of
# Even values update in dictionary
# Using update() + dictionary comprehension
  
# Initialize dictionary
test_dict = {'gfg' : 6, 'is' : 4, 'best' : 7}
  
# printing original dictionary
print("The original dictionary : " + str(test_dict))
  
# Using update() + dictionary comprehension
# Even values update in dictionary
test_dict.update((x, y * 3) for x, y in test_dict.items() if y % 2 == 0)
  
# printing result 
print("The dictionary after triple even key's value : " + str(test_dict))

Output :

The original dictionary : {'best': 7, 'is': 4, 'gfg': 6}
The dictionary after triple even key's value : {'best': 7, 'is': 12, 'gfg': 18}

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