filter() in python

filter() function is used to extract elements from an iterable (like a list, tuple or set) that satisfy a given condition. It works by applying a function to each element and keeping only those for which function returns True.

Example: This example shows how to keep only the words starting with the letter 'a' from a list of fruits.

['apple', 'avocado', 'apricot']

Explanation: function starts_a checks if a word begins with 'a' and filter() applies this function to each fruit and returns only matching ones.

Syntax

filter(function, iterable)

Parameters:

• function: tests each element and if return, True Keep the element, if False Discard the element
• iterable: Any iterable (list, tuple, set, etc.).

Return Value: A filter object (an iterator), which can be converted into a list, tuple, set, etc.

Examples

Example 1: This code defines a regular function to check if a number is even and then uses filter() to extract all even numbers from a list.

[2, 4, 6]

Explanation:

• even function checks if a number is divisible by 2.
• filter() applies this function to each item in a.
• Only even numbers are included in output.

Example 2: Below example uses a lambda function with filter() to select numbers divisible by 3.

[3, 6]

Example 3: Here, lambda function is used with filter() to keep only words that have more than 5 letters from a list of fruits.

['banana', 'cherry']

Example 4: This code uses filter() with None as the function to remove all falsy values (like empty strings, None and 0) from a list.

['apple', 'banana', 'cherry']

Explanation: filter(None, L) removes all falsy values (empty string, None and 0) and keeps only truthy ones.