How to Filter Even Numbers and Square Them in Python

Create two beginner-friendly helper functions that filter even numbers and compute squares of a number list using loops, then print the results along with the sum and average.

Easy Python 3.9+ Aug 9, 2026 Lists & loops 15 views 0 copies

loops filtering math beginner

Python code

23 lines

Python 3.9+

def get_even_numbers(numbers):
    evens = []
    for num in numbers:
        if num % 2 == 0:
            evens.append(num)
    return evens

def get_squares(numbers):
    squares = []
    for num in numbers:
        squares.append(num ** 2)
    return squares

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

even_numbers = get_even_numbers(numbers)
squares = get_squares(numbers)

print(f"Numbers: {numbers}")
print(f"Even numbers: {even_numbers}")
print(f"Squares: {squares}")
print(f"Total sum: {sum(numbers)}")
print(f"Average: {sum(numbers) / len(numbers)}")

Output

stdout

Numbers: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Even numbers: [2, 4, 6, 8, 10]
Squares: [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
Total sum: 55
Average: 5.5

How it works

This script defines two reusable functions that iterate through a list. get_even_numbers uses the modulo operator % to check if a number is divisible by 2 before appending it to a new list. get_squares computes each number's square with num ** 2 and stores it. After building the helpers, the code collects the transformed lists and prints them. The sum() function totals the list, and dividing by len() gives the average. Building small loops like these teaches how to accumulate results into a new list and makes data transforms clear and readable.

Common mistakes

Using `num / 2` instead of `num % 2` for even detection, which gives a float not a remainder.
Forgetting to initialize the result list before the loop, leading to a NameError.
Appending inside an `if` without proper indentation, causing logic errors or a syntax error.

Variations

Use a list comprehension: `[num for num in numbers if num % 2 == 0]` for filtering evens.
Use the `map()` function with a lambda to compute squares: `list(map(lambda x: x**2, numbers))`.

Real-world use cases

Filtering user-input IDs where only even-numbered records need processing.
Computing squared distances or areas for geometry calculations in a data pipeline.
Summarizing numeric sensor readings by filtering outliers and calculating averages.

How to Filter Even Numbers and Square Them in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Lists & loops

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