🚀 Day 97/150 – filter() Function in Python

The filter() function is a built-in Python function used to select elements from an iterable based on a condition. It returns only those elements for which the given function evaluates to True.

Syntax:

filter(function, iterable)

In this post, we'll explore four common examples of using the filter() function in Python.

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Method 1 – Using filter() with a Normal Function

Filter even numbers from a list using a normal function.

def is_even(num):
    return num % 2 == 0

numbers = [1, 2, 3, 4, 5, 6]

result = list(filter(is_even, numbers))

print(result)

Output

[2, 4, 6]

Explanation

• is_even() returns True if a number is even.

• filter() applies this function to every element in the list.

• Only the elements for which the function returns True are kept.

• list() converts the filter object into a list.

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Method 2 – Using filter() with a Lambda Function

Use a lambda function to write the filtering logic in a single line.

numbers = [10, 15, 20, 25, 30]

result = list(filter(lambda x: x > 20, numbers))

print(result)




Output

[25, 30]


Explanation

• lambda x: x > 20 checks whether each number is greater than 20.
  

• filter() keeps only the numbers that satisfy the condition.

• The result is converted into a list.

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Method 3 – Filtering Strings

Filter words whose length is greater than 5.

words = ["Python", "Java", "Programming", "Code"] result = list(filter(lambda word: len(word) > 5, words)) print(result)

Output

['Python', 'Programming']

Explanation

• len(word) > 5 checks the length of each word.

• filter() keeps only the words with more than 5 characters.

• This method is useful when working with text data.

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Method 4 – Taking User Input

Filter even numbers entered by the user.

numbers = list(map(int, input("Enter numbers separated by spaces: ").split()))

result = list(filter(lambda x: x % 2 == 0, numbers))

print("Even numbers:", result)






Sample Input

10 15 20 25 30

Output

Even numbers: [10, 20, 30]

Explanation

• input() reads the numbers as a string.

• split() separates them into a list.

• map(int, ...) converts each value to an integer.

• filter() selects only the even numbers.

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Comparison of Methods

Method	Best For
Normal Function	Reusable filtering logic
Lambda Function	Short and simple conditions
String Filtering	Filtering text data
User Input	Interactive programs

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🔥 Key Takeaways

• filter() selects elements that satisfy a condition.

• It returns a filter object, which is usually converted to a list using list().

• filter() works with both normal functions and lambda functions.

• It is commonly used to filter numbers, strings, and other collections.

• filter() makes code shorter and more readable than writing equivalent loops.

Stay tuned for Day 98 of the #150DaysOfPython series! 🚀