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

Challenge - 5 Problems

❓ Predict Output

intermediate

Sum of a list with a start value

What is the output of this code?

numbers = [1, 2, 3, 4]
result = sum(numbers, 10)
print(result)

Python

numbers = [1, 2, 3, 4]
result = sum(numbers, 10)
print(result)

A 24

B 10

C TypeError

D 20

💡 Hint

Remember that sum() can take a second argument as the starting value.

The sum() function adds all items in the list and then adds the start value 10. So, 1+2+3+4=10 plus 10 equals 20.

❓ Predict Output

intermediate

Sum of a tuple without start value

What is the output of this code?

values = (5, 10, 15)
print(sum(values))

Python

values = (5, 10, 15)
print(sum(values))

A TypeError

B 50

C 30

D 15

💡 Hint

sum() adds all numbers in the tuple by default starting from zero.

The sum of 5 + 10 + 15 is 30.

❓ Predict Output

advanced

Sum of a list of strings

What error does this code raise?

words = ['a', 'b', 'c']
print(sum(words))

Python

words = ['a', 'b', 'c']
print(sum(words))

A ValueError

B TypeError

C SyntaxError

D '' (empty string)

💡 Hint

sum() works only with numbers by default.

sum() cannot add strings because it expects numbers, so it raises a TypeError.

❓ Predict Output

advanced

Sum of a list with a non-zero start value and negative numbers

What is the output of this code?

nums = [-1, -2, -3]
print(sum(nums, 5))

Python

nums = [-1, -2, -3]
print(sum(nums, 5))

A -1

B 5

C TypeError

D -6

💡 Hint

sum() adds all numbers starting from the start value.

Sum of -1, -2, -3 is -6. Adding start value 5 gives 5 + (-6) = -1.

🧠 Conceptual

expert

Sum() with a list of lists

What error does this code raise?

list_of_lists = [[1, 2], [3, 4]]
print(sum(list_of_lists))

Python

list_of_lists = [[1, 2], [3, 4]]
print(sum(list_of_lists))

A TypeError

B ValueError

C SyntaxError

D [1, 2, 3, 4]

💡 Hint

sum() tries to add lists using + operator but needs a start value for lists.

sum() by default starts at 0, which cannot be added to a list, causing a TypeError.