filter() function in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this filter() example?

Consider the following Python code using filter(). What will be printed?

Python

numbers = [1, 2, 3, 4, 5, 6]
result = list(filter(lambda x: x % 2 == 0, numbers))
print(result)

A [1, 3, 5]

B [1, 2, 3, 4, 5, 6]

C [2, 4, 6]

D []

💡 Hint

filter() keeps items where the function returns True.

The lambda function returns True for even numbers only, so filter() keeps 2, 4, and 6.

❓ Predict Output

intermediate

What does this filter() call return?

What is the output of this code snippet?

Python

words = ['apple', 'banana', 'cherry', 'date']
result = list(filter(lambda w: len(w) > 5, words))
print(result)

A ['apple', 'banana', 'cherry']

B ['banana', 'cherry']

C ['date']

D ['apple', 'date']

💡 Hint

filter() keeps words longer than 5 letters.

Only 'banana' and 'cherry' have length greater than 5.

❓ Predict Output

advanced

What is the output of this filter() with None as function?

What will this code print?

Python

items = [0, 1, False, True, '', 'Hello', None, [], [1, 2]]
result = list(filter(None, items))
print(result)

A []

B [0, 1, False, True, '', 'Hello', None, [], [1, 2]]

C [False, True, 'Hello', None, [1, 2]]

D [1, True, 'Hello', [1, 2]]

💡 Hint

filter(None, iterable) removes all falsey values.

filter(None, ...) removes items that are false when converted to bool, keeping only truthy values.

❓ Predict Output

advanced

What is the output of this chained filter() example?

What will this code print?

Python

data = range(10)
result = list(filter(lambda x: x % 2 == 0, filter(lambda x: x > 4, data)))
print(result)

A [6, 8]

B [4, 6, 8]

C [0, 2, 4]

D [5, 6, 7, 8, 9]

💡 Hint

First filter keeps numbers > 4, second filter keeps even numbers.

Numbers > 4 are 5,6,7,8,9. Among these, even numbers are 6 and 8.

🧠 Conceptual

expert

Which option causes a TypeError when used with filter()?

Which of these options will cause a TypeError when passed as the function argument to filter()?

A An integer like 5

B None

C A function that returns True or False

D A lambda expression returning a boolean

💡 Hint

filter() expects a function or None as first argument.

Passing an integer instead of a function or None causes TypeError.