Lambda with map() in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of lambda with map() on a list

What is the output of this Python code?

Python

numbers = [1, 2, 3, 4]
result = list(map(lambda x: x * 3, numbers))
print(result)

A [1, 4, 9, 16]

B [1, 2, 3, 4]

C [3, 6, 9, 12]

D TypeError

💡 Hint

Remember map applies the function to each item in the list.

The lambda multiplies each number by 3, so the output list is each original number times 3.

❓ Predict Output

intermediate

Result of map with lambda and filter logic

What is the output of this code snippet?

Python

values = [0, 1, 2, 3, 4]
result = list(map(lambda x: x if x % 2 == 0 else 0, values))
print(result)

A SyntaxError

B [0, 1, 2, 3, 4]

C [0, 1, 0, 3, 0]

D [0, 0, 2, 0, 4]

💡 Hint

The lambda replaces odd numbers with zero.

For each number, if it is even, keep it; if odd, replace with 0. So 1 and 3 become 0.

❓ Predict Output

advanced

Output of nested lambda with map on strings

What does this code print?

Python

words = ['apple', 'banana', 'cherry']
result = list(map(lambda w: list(map(lambda c: c.upper(), w)), words))
print(result)

A ['APPLE', 'BANANA', 'CHERRY']

B [['A', 'P', 'P', 'L', 'E'], ['B', 'A', 'N', 'A', 'N', 'A'], ['C', 'H', 'E', 'R', 'R', 'Y']]

C [['apple'], ['banana'], ['cherry']]

D TypeError

💡 Hint

The inner map converts each character to uppercase.

Each word is mapped to a list of its uppercase letters, so the result is a list of lists of uppercase letters.

❓ Predict Output

advanced

Output of map with lambda and multiple iterables

What is the output of this code?

Python

a = [1, 2, 3]
b = [4, 5, 6]
result = list(map(lambda x, y: x + y, a, b))
print(result)

A [5, 7, 9]

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

C [4, 10, 18]

D TypeError

💡 Hint

map applies the lambda to pairs of elements from both lists.

The lambda adds corresponding elements: 1+4=5, 2+5=7, 3+6=9.

🧠 Conceptual

expert

Error raised by incorrect lambda syntax in map

What error does this code raise?

Python

result = list(map(lambda x: x * 2 if x > 2 for x in range(5)))

A SyntaxError

B TypeError

C NameError

D No error, outputs [6, 8]

💡 Hint

Check the lambda syntax and how map is used.

The lambda expression is invalid because it mixes a conditional expression with a for loop inside lambda, causing SyntaxError.

Practice

1.

What does the map() function do when used with a lambda in Python?

easy

A. Creates a new list without changing items

B. Filters items based on a condition

C. Applies the lambda function to each item in the list

D. Sorts the list items

Solution

1. Step 1: Understand the role of map()

   map() takes a function and a list, then applies the function to each item.

2. Step 2: Role of lambda with map()

   The lambda defines a quick function to apply to each item in the list.

3. Final Answer:

   Applies the lambda function to each item in the list -> Option C

4. Quick Check:

   map() + lambda = apply function to each item [OK]

Hint: Remember: map applies function to every list item [OK]

Common Mistakes:

• Thinking map filters items
• Assuming map sorts the list
• Believing map returns the original list unchanged

2.

Which of the following is the correct syntax to double each number in the list [1, 2, 3] using map() and lambda?

?

easy

A. map(lambda x: x * 2, [1, 2, 3])

B. list(map(lambda x: x * 2, [1, 2, 3]))

C. list(lambda x: x * 2, [1, 2, 3])

D. map([1, 2, 3], lambda x: x * 2)

Solution

1. Step 1: Check map() syntax

   map() takes a function first, then the iterable (list).

2. Step 2: Convert map object to list

   To see results, wrap map() with list().

3. Final Answer:

   list(map(lambda x: x * 2, [1, 2, 3])) -> Option B

4. Quick Check:

   Correct syntax = list(map(lambda x: x * 2, list)) [OK]

Hint: Use list() around map() to see results [OK]

Common Mistakes:

• Forgetting to convert map to list
• Swapping arguments in map()
• Using lambda outside map() incorrectly

3.

What is the output of the following code?

nums = [1, 2, 3, 4]
result = list(map(lambda x: x + 1, nums))
print(result)

medium

A. [2, 3, 4, 5]

B. [1, 2, 3, 4]

C. [0, 1, 2, 3]

D. Error

Solution

1. Step 1: Understand the lambda function

   The lambda adds 1 to each number in the list.

2. Step 2: Apply lambda to each item in nums

   Each number 1,2,3,4 becomes 2,3,4,5 respectively.

3. Final Answer:

   [2, 3, 4, 5] -> Option A

4. Quick Check:

   Each item +1 = [2,3,4,5] [OK]

Hint: Add 1 to each item with lambda x: x + 1 [OK]

Common Mistakes:

• Forgetting to convert map to list before print
• Confusing addition with multiplication
• Expecting original list unchanged

4.

Find the error in this code snippet:

numbers = [1, 2, 3]
result = map(lambda x: x ** 2, numbers)
print(result)

medium

A. map() requires two arguments but only one given

B. Lambda syntax is incorrect

C. List 'numbers' is not defined

D. Missing list() to convert map object before printing

Solution

1. Step 1: Check map() usage

   map() returns a map object, not a list.

2. Step 2: Printing map object directly

   Printing map object shows memory address, not values; convert to list first.

3. Final Answer:

   Missing list() to convert map object before printing -> Option D

4. Quick Check:

   Use list() to see map results [OK]

Hint: Wrap map() with list() before printing [OK]

Common Mistakes:

• Trying to print map object directly
• Thinking lambda syntax is wrong
• Assuming map needs more arguments

5.

You have a list of strings representing numbers: ['1', '2', '3', '4']. Using map() and lambda, how do you convert this list to integers and then add 10 to each number?

hard

A. list(map(lambda x: int(x) + 10, ['1', '2', '3', '4']))

B. list(map(lambda x: x + 10, ['1', '2', '3', '4']))

C. list(map(int(x) + 10, ['1', '2', '3', '4']))

D. list(map(lambda x: int(x + 10), ['1', '2', '3', '4']))

Solution

1. Step 1: Convert strings to integers inside lambda

   Use int(x) to convert each string to an integer.

2. Step 2: Add 10 to each converted integer

   Inside lambda, add 10 to the integer value.

3. Final Answer:

   list(map(lambda x: int(x) + 10, ['1', '2', '3', '4'])) -> Option A

4. Quick Check:

   Convert then add 10 = list(map(lambda x: int(x)+10, list)) [OK]

Hint: Convert string to int inside lambda before adding [OK]

Common Mistakes:

• Adding 10 to string without conversion
• Incorrect lambda syntax
• Trying to call int() outside lambda in map