Python | Multiply Dictionary Value by Constant

Sometimes, while working with dictionaries, we can have a use-case in which we require to multiply 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 1 and then the product is possible. By this way the problem of non-existing key can be avoided. 

Python3

# Python3 code to demonstrate working of
# Multiply Dictionary Value by Constant
# 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()
# Multiply Dictionary Value by Constant
test_dict['best'] = test_dict.get('best', 1) * K

# printing result
print("Dictionary after the multiplication of key : " + str(test_dict))

Output : 

The original dictionary : {'for': 4, 'is': 2, 'CS': 5, 'gfg': 1}
Dictionary after the multiplication of key : {'for': 4, 'is': 2, 'CS': 5, 'best': 5, '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

# Python3 code to demonstrate working of
# Multiply Dictionary Value by Constant
# 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()
# Multiply Dictionary Value by Constant
test_dict['best'] *= K

# printing result
print("Dictionary after the multiplication of key : " + str(dict(test_dict)))

Output : 

The original dictionary : {}
Dictionary after the multiplication of key : {'best': 0}

Method #3: Using dict.update()
Using dict.update() method, we can add an element to the dictionary, based on the condition if it exists or not.

Python3

# Python3 code to demonstrate working of
# Multiply Dictionary Value by Constant
# Using update()

# 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 update()
# Multiply Dictionary Value by Constant
test_dict.update({'best' : test_dict.get('best', 1) * K})

# printing result
print("Dictionary after the multiplication of key : " + str(test_dict))

Output

The original dictionary : {'gfg': 1, 'is': 2, 'for': 4, 'CS': 5}
Dictionary after the multiplication of key : {'gfg': 1, 'is': 2, 'for': 4, 'CS': 5, 'best': 5}

Time complexity: O(1)

Auxiliary space: O(1)