Filter string in list Python

filter[] Syntax

Its syntax 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[]

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 # converting to tuple vowels = tuple[filtered_vowels] print[vowels]

Output

['a', 'e', 'i', 'o', 'u']

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[]

numbers = [1, 2, 3, 4, 5, 6, 7] # the lambda function returns True for even numbers even_numbers_iterator = filter[lambda x: [x%2 == 0], numbers] # converting to list even_numbers = list[even_numbers_iterator] print[even_numbers]

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[]

# random list random_list = [1, 'a', 0, False, True, '0'] #converting to list filtered_list = list[filtered_iterator] print[filtered_list]

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.