Python | Selective Keys Summation

• Last Updated : 23 Jan, 2020

Sometimes while working with Python dictionaries, we might have a problem in which we require to just sum the selective key values from the dictionary. This problem can occur in web development domain. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using list comprehension + get() + sum()
The combination of above functions can be used to perform this particular task. In this, we access the values using the get method and traverse the dictionary using list comprehension. We perform summation using sum().

 # Python3 code to demonstrate working of # Selective Keys Summation# Using list comprehension + get() + sum()   # Initialize dictionary test_dict = {'gfg' : 1, 'is' : 2, 'best' : 3, 'for' : 4, 'CS' : 5}   # printing original dictionary print("The original dictionary : " + str(test_dict))   # Initialize key list key_list = ['gfg', 'best', 'CS']   # Using list comprehension + get() + sum()# Selective Keys Summationres = sum([test_dict.get(key) for key in key_list])       # printing result print("The summation of Selective keys : " + str(res))
Output :
The original dictionary : {'CS': 5, 'best': 3, 'is': 2, 'gfg': 1, 'for': 4}
The summation of Selective keys : 9

Method #2 : Using itemgetter() + sum()
This single function can be used to perform this particular task. It is built in to perform this specific task. It takes chain of keys and returns the corresponding values as a tuple which can be type casted. We perform summation using sum().

 # Python3 code to demonstrate working of # Selective Keys Summation# Using itemgetter() + sum()from operator import itemgetter   # Initialize dictionary test_dict = {'gfg' : 1, 'is' : 2, 'best' : 3, 'for' : 4, 'CS' : 5}   # printing original dictionary print("The original dictionary : " + str(test_dict))   # Initialize key list key_list = ['gfg', 'best', 'CS']   # Using itemgetter() + sum()# Selective Keys Summationres = sum(list(itemgetter(*key_list)(test_dict)))       # printing result print("The summation of Selective keys : " + str(res))
Output :
The original dictionary : {'CS': 5, 'best': 3, 'is': 2, 'gfg': 1, 'for': 4}
The summation of Selective keys : 9

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