In this tutorial, we will learn about the Python filter() function with the help of examples.
The filter() function extracts elements from an iterable (list, tuple etc.) for which a function returns True.
Example
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
# returns True if number is even
def check_even(number):
if number % 2 == 0:
return True
return False
# Extract elements from the numbers list for which check_even() returns True
even_numbers_iterator = filter(check_even, numbers)
# converting to list
even_numbers = list(even_numbers_iterator)
print(even_numbers)
# Output: [2, 4, 6, 8, 10]
filter() Syntax
Its syntax is:
filter(function, iterable)
filter() Arguments
The filter() function takes two arguments:
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()
letters = ['a', 'b', 'd', 'e', 'i', 'j', 'o']
# a function that returns True if letter is vowel
def filter_vowels(letter):
vowels = ['a', 'e', 'i', 'o', 'u']
return True if letter in vowels else False
filtered_vowels = filter(filter_vowels, letters)
# converting to tuple
vowels = tuple(filtered_vowels)
print(vowels)
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.
