Python | Increment value in dictionary

Sometimes, while working with dictionaries, we can have a use-case in which we require to increment a particular key’s value 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 increment is possible. By this way the problem of non-existing key can be avoided. 

Python3

# Python3 code to demonstrate working of
# Increment value in dictionary
# Using get()

# Initialize dictionary
test_dict = {'gfg' : 1, 'is' : 2, 'for' : 4, 'CS' : 5}

# printing original dictionary
print("The original dictionary : " +  str(test_dict))

# Using get()
# Increment value in dictionary
test_dict['best'] = test_dict.get('best', 0) + 3

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

Output : 

The original dictionary : {‘is’: 2, ‘CS’: 5, ‘for’: 4, ‘gfg’: 1} Dictionary after the increment of key : {‘is’: 2, ‘CS’: 5, ‘for’: 4, ‘best’: 3, ‘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
# Increment value in dictionary
# Using defaultdict()
from collections import defaultdict

# Initialize dictionary
test_dict = defaultdict(int)

# printing original dictionary
print("The original dictionary : " +  str(dict(test_dict)))

# Using defaultdict()
# Increment value in dictionary
test_dict['best'] += 3

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

Output : 

The original dictionary : {} Dictionary after the increment of key : {‘best’: 3}

Method #3 : Using Counter()
Using Counter() is another way to increment the value in dictionary.

Python3

# Python3 code to demonstrate working of
# Increment value in dictionary
# Using Counter()
from collections import Counter

# Initialize dictionary
test_dict = {'gfg' : 1, 'is' : 2, 'for' : 4, 'CS' : 5}

# printing original dictionary
print("The original dictionary : " +  str(test_dict))

# Using Counter()
# Increment value in dictionary
val = Counter(test_dict)
val.update({'best':3})

# printing result
print("Dictionary after the increment of key : " + str(dict(val)))
#This code is contributed by Edula Vinay Kumar Reddy

Output

The original dictionary : {'gfg': 1, 'is': 2, 'for': 4, 'CS': 5}
Dictionary after the increment of key : {'gfg': 1, 'is': 2, 'for': 4, 'CS': 5, 'best': 3}

Time Complexity : O(1)
Auxiliary Space : O(N)