5 Best Ways to Sum Dictionary Values in Python

Problem Formulation and Solution Overview

In this article, you’ll learn how to Sum Dictionary Values in Python.

To make it more fun, we have the following running scenario:

As a Python Freelancer, you would like to know how much money you made over the past few months. This data is stored in a Dictionary format. This total can be found by summing up (tallying) the Dictionary values.

💬 Question: How would we write Python code to sum dictionary values in Python?

We can accomplish this task by one of the following options:

• Method 1: Use sum() and dict.values()
• Method 2: Use sum() and a Generator Expression
• Method 3: Use functools.reduce() and a Lambda
• Method 4: Use sum() and list()
• Method 5: Use a simple for loop and aggregate

Method 1: Use sum() and dict.values()

You can use the functions sum() and dict.values() to sum all values of a Python dictionary with the expression sum(dict.values()).

Here’s how this applies to our example scenario:

wages = {'01': 910.56, '02': 1298.68, '03': 1433.99, '04': 1050.14, '05': 877.67}
total = sum(wages.values())
print('Total Wages: ${0:,.2f}'.format(total))

This code declares a Dictionary, wages containing five (5) key:value pairs of monthly income.

Option 1 above tallies the extracted values and saves to total. Then using format(), the output is modified to display a Dollar sign ($), a comma (if needed), and restrict the output to two (2) decimal places.

OR

total = round(sum(wages.values()), 2)
print(total)

Option 2 above tallies the extracted values, rounds the result to two (2) decimal places, and saves to total. The result is output to the terminal as is.

Method 2: Use sum() and Generator Expression

You can combine the built-in sum() function with a simple generator expression to sum all values in a Python dictionary with the expression sum(my_dict[item] for item in my_dict).

Here’s the example:

wages = {'01': 910.56, '02': 1298.68, '03': 1433.99, '04': 1050.14, '05': 877.67}
total = sum(wages[item] for item in wages)
print('Total Wages: ${0:,.2f}'.format(total))

This code declares a Dictionary, wages containing five (5) key:value pairs of monthly income.

A one-line for loop is used to navigate each Dictionary item (value) and tally the items. The result saves to total.

Then, format() is used to modify the output to display a Dollar sign ($), a comma (if needed), and restrict the output to two (2) decimal places.

Method 3: Use a Lambda

An alternative way to sum over Python dictionary values is to use the functools.reduce() method in combination with a lambda function in the expression functools.reduce(lambda tot, v: tot+my_dict[v], my_dict, 0).

Here’s what that looks like in our example scenario:

wages = {'01': 910.56, '02': 1298.68, '03': 1433.99, '04': 1050.14, '05': 877.67}
total = functools.reduce(lambda tot, v: tot+wages[v], wages, 0)
print(total)

First, this code declares a Dictionary, wages containing five (5) key:value pairs of monthly income.

Then, the functools.reduce() function is used with a Lambda to tally the wages. This result saves to total and is output to the terminal as is.

Output

Method 4: Use a Generator

To sum all values in a Python dictionary, use sum() and a list representation of the dictionary values obtained with my_dict.values() and using list() for the conversion.

wages = {'01': 910.56, '02': 1298.68, '03': 1433.99, '04': 1050.14, '05': 877.67}
print(sum(list(wages.values())))

First, this code declares a Dictionary, wages containing five (5) key:value pairs of monthly income.

Then, the values are converted into a List format. Finally, the sum() function is applied to this List and output to the terminal.

Output

Method 5: Simple For Loop

You can sum all values in a Python dictionary by iterating over all dictionary values using a for loop and adding them one by one.

Here’s our running example:

wages = {'01': 910.56, '02': 1298.68, '03': 1433.99,
         '04': 1050.14, '05': 877.67}
total = 0
for value in wages.values():
    total += value

print(total)
# 5571.04

This is not the most Pythonic approach, however. A generator expression would be more concise and more readable.

Summary

These five (5) methods of summing Dictionary values should give you enough information to select the best one for your coding requirements.

Good Luck & Happy Coding!