Python Program to Find Sum of All Elements in List

You can find the sum of all elements in a list in Python by using the built-in sum() function like total = sum(your_list).

Examples

Input[1, 2, 3]

Output6

Input[10, -5, 7, 3]

Output15

Input[]

Output0

How to Think About It

To find the sum of all elements in a list, think of adding each number one by one until you have added every element. You start with zero and keep adding each element to this total until the list ends.

Algorithm

1

Start with a total sum set to zero.

2

Go through each element in the list one by one.

3

Add the current element's value to the total sum.

4

After all elements are added, return or print the total sum.

Code

python

numbers = [1, 2, 3, 4, 5]
total = sum(numbers)
print(total)

Output

15

Dry Run

Let's trace the list [1, 2, 3, 4, 5] through the code using sum().

1

Initialize list

numbers = [1, 2, 3, 4, 5]

2

Call sum()

sum(numbers) adds 1 + 2 + 3 + 4 + 5

3

Calculate total

total = 15

4

Print result

print(total) outputs 15

Iteration	Current Element	Running Total
1	1	1
2	2	3
3	3	6
4	4	10
5	5	15

Why This Works

Step 1: Using sum() function

The sum() function automatically adds all elements in the list without needing a loop.

Step 2: Starting total at zero

The function starts adding from zero, so if the list is empty, the result is zero.

Step 3: Adding each element

Each element is added one by one to the total until all elements are processed.

Alternative Approaches

Using a for loop

python

numbers = [1, 2, 3, 4, 5]
total = 0
for num in numbers:
    total += num
print(total)

This method shows the addition process step-by-step but is longer than using sum().

Using reduce() from functools

python

from functools import reduce
numbers = [1, 2, 3, 4, 5]
total = reduce(lambda x, y: x + y, numbers)
print(total)

This uses a functional programming style but is less readable for beginners.

Complexity: O(n) time, O(1) space

Time Complexity

The program must visit each element once to add it, so the time grows linearly with the list size.

Space Complexity

Only a single variable is used to store the sum, so extra space does not grow with input size.

Which Approach is Fastest?

Using sum() is fastest and most readable; loops are clear but longer; reduce() is less common and slightly slower.

Approach	Time	Space	Best For
sum() function	O(n)	O(1)	Simple and fast summing
for loop	O(n)	O(1)	Learning how addition works step-by-step
reduce() function	O(n)	O(1)	Functional programming style