Print even numbers in a list - Python

Getting even numbers from a list in Python allows you to filter out all numbers that are divisible by 2. For example, given the list a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], you might want to extract the even numbers [2, 4, 6, 8, 10]. There are various efficient methods to extract even numbers from a list. Let's explore different methods to do this efficiently.

Using List comprehension

List comprehensions is an efficient way to filter elements from a list. They are generally considered more Pythonic and faster than traditional loops.

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

res = [val for val in a if val % 2 == 0]
print(res)

[2, 4, 6, 8, 10]

Explanation: [val for val in a if val % 2 == 0] iterates through the list a and selects only the even numbers.

Using filter()

filter() function provides a functional programming approach to filter elements from a list. It can be a bit less intuitive compared to list comprehensions, but it is still very useful.

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

res = list(filter(lambda val: val % 2 == 0, a))
print(res)

[2, 4, 6, 8, 10]

Explanation: filter() function takes lambda function that tests each element in the list. lambda val: val % 2 == 0 returns True for even numbers, which are then included in the final list. We convert the result to a list using list().

Using loop

Using a traditional for loop is the most straightforward method, but it is generally less efficient and more verbose compared to other methods.

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

for val in a:
    if val % 2 == 0:
        print(val, end=" ")

2 4 6 8 10 

Explanation: For loop iterates through each element in the list a. If the element is divisible by 2 (even number), it is printed.

Using Bitwise AND operator

This is a low-level, bitwise approach to check if a number is even. It works by performing a bitwise AND operation with 1, which will return 0 for even numbers and 1 for odd numbers.

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

res = [val for val in a if val & 1 == 0]
print(res)

[2, 4, 6, 8, 10]

Explanation: expression val & 1 == 0 uses the bitwise AND operator to check if the least significant bit of a number is 0. Even numbers have their least significant bit as 0, so the condition evaluates to True for even numbers.

Related Articles

• List comprehension
• filter()
• Loop
• Bitwise AND operator