Filter in Python

Python : Filter

What is Filter in Python? In Python, filter() is a built-in function that can be used to filter out items from a sequence based on a given condition. It takes two arguments: a function and a sequence. The function is applied to each element in the sequence, and if the function returns True, that element is included in the result; if it returns False, the element is excluded.

Filter Syntax in Python:

filter(function, sequence)

Filter Parameters in Python:

• function: The function to be applied to each element in the sequence. It takes one argument and returns a Boolean value.
• sequence: The sequence to be filtered.
• Return Value: A filtered iterable object containing only the elements from the original sequence for which the function returned True.

Filter use cases in Python?

1. Filtering even numbers from a list

   # define a list of numbers
   numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
   
   # define a function to filter even numbers
   def is_even(num):
       return num % 2 == 0
   
   # use filter to get only even numbers
   even_numbers = list(filter(is_even, numbers))
   
   # print the result
   print(even_numbers)
   # Output: [2, 4, 6, 8, 10]
   

2. Filtering strings with length greater than 5

   # define a list of strings
   fruits = ['apple', 'banana', 'kiwi', 'orange', 'pear', 'strawberry']
   
   # define a function to filter strings with length greater than 5
   def is_long_string(s):
       return len(s) > 5
   
   # use filter to get only long strings
   long_strings = list(filter(is_long_string, fruits))
   
   # print the result
   print(long_strings)
   # Output: ['banana', 'orange', 'strawberry']
   

3. Filtering a dictionary based on a condition

   # define a dictionary of people and their ages
   ages = {'Alice': 25, 'Bob': 30, 'Charlie': 35, 'David': 40}
   
   # define a function to filter people whose age is greater than 30
   def is_above_thirty(age):
       return age > 30
   
   # use filter to get only people above 30
   above_thirty = dict(filter(lambda x: is_above_thirty(x[1]), ages.items()))
   
   # print the result
   print(above_thirty)
   # Output: {'Charlie': 35, 'David': 40}