Python filter()

filter() Syntax

The syntax of filter() is:

filter(function, iterable)

filter() Arguments

The filter() function takes two arguments:

• function - a function
• iterable - an iterable like sets, lists, tuples etc.

filter() Return Value

The filter() function returns an iterator.

Note: You can easily convert iterators to sequences like lists, tuples, strings etc.

Example 1: Working of filter()

Output

('a', 'e', 'i', 'o')

Here, the filter() function extracts only the vowel letters from the letters list. Here's how this code works:

• Each element of the letters list is passed to the filter_vowels() function.
• If filter_vowels() returns True, that element is extracted otherwise it's filtered out.

Note: It's also possible to filter lists using a loop, however, using the filter() function is much more cleaner.

Example 2: Using Lambda Function Inside filter()

Output

[2, 4, 6]

Here, we have directly passed a lambda function inside filter().

Our lambda function returns True for even numbers. Hence, the filter() function returns an iterator containing even numbers only.

Example 3: Using None as a Function Inside filter()

Output

[1, 'a', True, '0']

When None is used as the first argument to the filter() function, all elements that are truthy values (gives True if converted to boolean) are extracted.