How to use sum() Function in Python?

Ayushi Trivedi 31 May, 2024
4 min read


In this article, you’ll discover an in-depth exploration of the sum() function in Python, a crucial built-in utility for aggregating numbers across various iterable types. We begin by explaining the fundamental syntax and parameters of the sum() function, followed by detailed examples showcasing its application to lists, dictionaries, sets, and tuples. Additionally, you’ll learn about error handling to prevent common pitfalls and see practical scenarios, such as calculating averages, where sum() proves invaluable. This guide aims to enhance your understanding and usage of sum() in everyday programming tasks, making your code more efficient and readable.

How to use sum() Function in Python?

What is sum() Function?

You may compute the sum of the numbers in an iterable using Python’s robust built-in sum() function. In jobs involving data analysis and processing, this function is commonly utilized. Let us understand the syntax of sum() function.

Syntax of sum() Function

The sum() function syntax is straightforward:

sum(iterable, start)
  • iterable: Any iterable holding numerical values, such as a list, tuple, set, dictionary, etc., can be this.
  • start: This optional argument adds a specified value to the sum of the iterable’s values. In the absence of one, it defaults to 0.

Simplified Syntax Variations

  • sum(a): Calculates the total number in the list a, with 0 as the initial value by default.
  • sum(a, start): Computes the sum of the numbers in the list a and adds the start value to the result.

Basic Usage

Let’s start with a basic example where we sum a list of numbers to better understand how the sum() function functions. This basic example will illustrate the core functionality of sum() in a straightforward manner.

numbers = [1, 2, 3, 4, 5]
total = sum(numbers)
print(total)  # Output: 15

Using the start Parameter

The start parameter allows you to add a value to the sum of the iterable. Here’s how you can use it:

numbers = [1, 2, 3, 4, 5]
total = sum(numbers, 10)
print(total)  # Output: 25

Examples of Using sum()

Let us now explore some examples of using sum().

Summing Numbers in a List

Let’s start with a basic example of summing numbers in a list.

expenses = [200, 150, 50, 300]
total_expenses = sum(expenses)
print(total_expenses)  # Output: 700

Summing Values in a Dictionary

You can sum the values of a dictionary using the values() method.

my_dict = {'x': 21, 'y': 22, 'z': 23}
total = sum(my_dict.values())
print(total)  # Output: 66

Summing Elements in a Set

Sets, like lists, can be summed directly.

unique_numbers = {12, 14, 15}
total_unique = sum(unique_numbers)
print(total_unique)  # Output: 39

Summing Elements in a Tuple

Tuples, similar to lists, can also be summed.

scores = (90, 85, 88, 92)
total_scores = sum(scores)
print(total_scores)  # Output: 355

Summing Numbers Using a For Loop

Although the sum() function is convenient, you can also sum numbers manually using a for loop.

numbers = [100, 200, 300, 400, 500]

# Initialize the sum to 0
total = 0

# Iterate through the list and add each number to the total
for num in numbers:
    total += num

print("The sum of the numbers is:", total)  # Output: 1500

Summing with a Generator Expression

Generator expressions can be used to sum a series of numbers generated on the fly:

total = sum(i for i in range(1, 6))
print(total)  # Output: 15

Summing the Elements of a List of Lists

Sometimes, you may have a list of lists and want to sum the elements within each list. Here’s how you can do it:

list_of_lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
total = sum(sum(inner_list) for inner_list in list_of_lists)
print(total)  # Output: 45

Advanced Applications

Let us explore some advanced applications of sum() function.

Summing Non-Numeric Values

While sum() is primarily used for numeric values, you can use it in conjunction with other functions to sum non-numeric values. For example, summing the lengths of strings in a list:

words = ["apple", "banana", "cherry"]
total_length = sum(len(word) for word in words)
print(total_length)  # Output: 16

Summing with Conditional Logic

You can incorporate conditional logic within a generator expression to sum values that meet certain criteria:

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
total_even = sum(n for n in numbers if n % 2 == 0)
print(total_even)  # Output: 30

Error Handling

The sum() function raises a TypeError if the iterable contains non-numeric values.

array1 = ["apple"]

    # Attempt to sum the list of strings
    total = sum(array1)
except TypeError as e:
    print(e)  # Output: unsupported operand type(s) for +: 'int' and 'str'

Practical Application

Let us now look into the practical applications of sum() function.

Summing the Ages of a List of People

class Person:
    def __init__(self, name, age): = name
        self.age = age

people = [Person("Alice", 30), Person("Bob", 25), Person("Charlie", 35)]

# Calculate the total sum of ages
total_age = sum(person.age for person in people)
print(total_age)  # Output: 90

Financial Calculations

Sum() can be used for financial calculations, such as computing the total expenses or income over a period.

Calculating Total Expenses:

expenses = {
    'rent': 1200,
    'groceries': 300,
    'utilities': 150,
    'entertainment': 100

# Calculate the total sum of expenses
total_expenses = sum(expenses.values())
print(total_expenses)  # Output: 1750

Calculating Yearly Income:

monthly_income = [2500, 2700, 3000, 3200, 2900, 3100, 2800, 2600, 3300, 3500, 3400, 3600]

# Calculate the total sum of yearly income
yearly_income = sum(monthly_income)
print(yearly_income)  # Output: 37600


For adding up the numbers in different iterables, Python’s sum() method provides a flexible and effective tool. It is a vital tool for any programmer’s toolset because of its simplicity of usage and Python’s strong error handling. The sum() function makes aggregation simpler and enables straightforward, short code, regardless of whether one is working with lists, tuples, sets, or dictionaries.

Ayushi Trivedi 31 May, 2024

Frequently Asked Questions

Lorem ipsum dolor sit amet, consectetur adipiscing elit,

Responses From Readers