Python Program to Find Average of Numbers

To find the average of numbers in Python, sum the numbers using sum() and divide by the count using len(), like average = sum(numbers) / len(numbers).

Examples

Input[10, 20, 30]

Output20.0

Input[5, 15, 25, 35]

Output20.0

Input[100]

Output100.0

How to Think About It

To find the average, first add all the numbers together to get the total sum. Then count how many numbers there are. Finally, divide the total sum by the count to get the average value.

Algorithm

1

Get the list of numbers

2

Calculate the sum of all numbers

3

Count how many numbers are in the list

4

Divide the sum by the count to get the average

5

Return or print the average

Code

python

numbers = [10, 20, 30]
average = sum(numbers) / len(numbers)
print(average)

Output

20.0

Dry Run

Let's trace the example [10, 20, 30] through the code

1

Input list

numbers = [10, 20, 30]

2

Calculate sum

sum(numbers) = 10 + 20 + 30 = 60

3

Count numbers

len(numbers) = 3

4

Calculate average

average = 60 / 3 = 20.0

5

Print result

Output: 20.0

Step	Sum	Count	Average
Initial	-	-	-
Calculate sum	60	-	-
Count numbers	60	3	-
Calculate average	60	3	20.0

Why This Works

Step 1: Sum all numbers

Using sum() adds all numbers together to get the total.

Step 2: Count numbers

Using len() counts how many numbers are in the list.

Step 3: Divide sum by count

Dividing total sum by count gives the average value.

Alternative Approaches

Using a loop to calculate sum

python

numbers = [10, 20, 30]
sum_numbers = 0
for num in numbers:
    sum_numbers += num
average = sum_numbers / len(numbers)
print(average)

This method shows the manual way to sum numbers but is longer than using built-in sum().

Using statistics.mean() function

python

import statistics
numbers = [10, 20, 30]
average = statistics.mean(numbers)
print(average)

This uses Python's built-in statistics module for a clean and readable solution.

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

Time Complexity

Calculating the sum requires visiting each number once, so it takes O(n) time where n is the number of elements.

Space Complexity

The program uses a fixed amount of extra space regardless of input size, so space complexity is O(1).

Which Approach is Fastest?

Using built-in sum() is fastest and most readable; manual loops are slower and more verbose; statistics.mean() is clean but adds import overhead.

Approach	Time	Space	Best For
Built-in sum() and len()	O(n)	O(1)	Simple and fast average calculation
Manual loop sum	O(n)	O(1)	Learning how summing works internally
statistics.mean()	O(n)	O(1)	Clean code with standard library support