Python - Filter even values from a list

As part of data analysis, we often need to filter values from a list meeting certain criteria. In this article, we'll see how to filter out only the even values from a list.

To identify even numbers, we check if a number is divisible by 2 (remainder is zero when divided by 2). Python provides several approaches to filter even values from a list.

Using for Loop

This is the simplest way to iterate through each element and check for divisibility by 2 ?

numbers = [33, 35, 36, 39, 40, 42]

even_numbers = []

for n in numbers:
    if n % 2 == 0:
        even_numbers.append(n)

print(even_numbers)

[36, 40, 42]

Using While Loop

When working with lists of unknown lengths, a while loop with the len() function provides more control over iteration ?

numbers = [33, 35, 36, 39, 40, 42]

even_numbers = []
i = 0

while i < len(numbers):
    if numbers[i] % 2 == 0:
        even_numbers.append(numbers[i])
    i += 1

print(even_numbers)

[36, 40, 42]

Using filter() with Lambda

The filter() function combined with a lambda expression provides a functional programming approach ?

numbers = [33, 35, 36, 39, 40, 42]

is_even = lambda x: x % 2 == 0
even_numbers = list(filter(is_even, numbers))

print(even_numbers)

[36, 40, 42]

Using List Comprehension

List comprehension offers the most Pythonic and concise way to filter even numbers ?

numbers = [33, 35, 36, 39, 40, 42]

even_numbers = [n for n in numbers if n % 2 == 0]

print(even_numbers)

[36, 40, 42]

Comparison

Conclusion

List comprehension is the most efficient and Pythonic way to filter even numbers. Use filter() for functional programming style, and loops when you need more complex logic or are learning Python basics.