The filter() function returns an iterator where the items are filtered through a function to test if the item is accepted or not.
Syntax
filter(function, iterable)filter() Parameters
Python filter() function parameters:
| Parameter | Condition | Description |
|---|---|---|
function |
Required | A Function to be run for each item in the iterable |
iterable |
Required | The iterable to be filtered |
filter() Return Value
Python filter() function returns an iterator yielding the items of the iterable for which the function returns True.
Examples
Example 1: filter even numbers from List
def is_even(n):
return n % 2 == 0
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
even_numbers = filter(is_even, numbers)
print(list(even_numbers)) # Output: [2, 4, 6]output
[2, 4, 6]Example 2: filter vowels from List
letters = ['a', 'b', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
def filter_vowels(letter):
vowels = ['a', 'e', 'i', 'o', 'u']
if letter in vowels:
return True
else:
return False
filtered_vowels = filter(filter_vowels, letters)
vowels = tuple(filtered_vowels)
print(vowels) # Output: ('a', 'e', 'i', 'o', 'u')output
('a', 'e', 'i', 'o', 'u')Example 3: filter words string that starts with 'p'
def starts_with_p(s):
return s[0].lower() == 'p'
words = ["python", "java", "c++", "perl", "pascal"]
p_words = filter(starts_with_p, words) # Output: ['python', 'pascal']output
['python', 'pascal']Example 4: filter() function with Lambda
You can also use the Python filter() function with the lambda function.
For example:
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
even_numbers_iterator = filter(lambda x: (x%2 == 0), numbers)
even_numbers = list(even_numbers_iterator)
print(even_numbers) # Output: [2, 4, 6, 8, 10]output
[2, 4, 6, 8, 10]Example 5: use None as a Function inside filter() function
When None is used as the first argument to the filter() function, it extracts all elements that evaluate to True when converted to boolean.
For example:
random_list = [1, 'a', 0, False, True, '0']
filtered_iterator = filter(None, random_list)
filtered_list = list(filtered_iterator)
print(filtered_list) # Output: [1, 'a', True, '0']output
[1, 'a', True, '0']