sum() function in Python - Mini Project: Build & Apply

Using the sum() Function in Python

📖 Scenario: You are helping a small shop owner who wants to quickly add up the prices of items sold in a day.

🎯 Goal: Build a simple program that uses the sum() function to add all the prices in a list and show the total sales.

📋 What You'll Learn

Create a list of item prices

Create a variable to hold the total sum

Use the sum() function to add all prices

Print the total sum

💡 Why This Matters

🌍 Real World

Adding prices or scores quickly is common in shops, schools, and many daily tasks.

💼 Career

Knowing how to sum values helps in data analysis, finance, and programming jobs where totals are needed.

1

Create a list of item prices

Create a list called prices with these exact values: 10.5, 23.99, 5.0, 12.75, and 7.25.

Python

# Create the list prices with the given values
# Your code here

Hint

Use square brackets [] to create a list and separate values with commas.

2

Create a variable to hold the total sum

Create a variable called total and set it to 0.

Python

prices = [10.5, 23.99, 5.0, 12.75, 7.25]
# Create a variable total and set it to 0
# Your code here

Hint

Just write total = 0 to start with zero.

3

Use the sum() function to add all prices

Use the sum() function on the prices list and assign the result to the variable total.

Python

prices = [10.5, 23.99, 5.0, 12.75, 7.25]
total = 0
# Use sum() on prices and assign to total
# Your code here

Hint

Use sum(prices) to add all numbers in the list.

4

Print the total sum

Write a print() statement to display the text Total sales: followed by the value of total.

Python

prices = [10.5, 23.99, 5.0, 12.75, 7.25]
total = 0
total = sum(prices)
# Print the total sales with the total value
# Your code here

Hint

Use an f-string like print(f"Total sales: {total}") to show the result.

Practice

1. What does the sum() function do in Python?

easy

A. Counts the number of elements in an iterable

B. Multiplies all numbers in an iterable

C. Adds all numbers in an iterable and returns the total

D. Finds the largest number in an iterable

Solution

1. Step 1: Understand the purpose of sum()

   The sum() function takes an iterable like a list or tuple and adds all its numbers together.

2. Step 2: Compare options with the function's behavior

   Only Adds all numbers in an iterable and returns the total correctly describes adding all numbers and returning the total.

3. Final Answer:

   Adds all numbers in an iterable and returns the total -> Option C

4. Quick Check:

   sum() adds numbers [OK]

Hint: Remember: sum() adds, not multiplies or counts [OK]

Common Mistakes:

• Confusing sum() with multiplication
• Thinking sum() counts elements
• Assuming sum() finds max value

2. Which of the following is the correct syntax to sum numbers in a list nums starting from 10?

easy

A. sum(nums, 10)

B. sum(10, nums)

C. sum(nums + 10)

D. sum(start=10, nums)

Solution

1. Step 1: Recall the sum() function signature

   The sum() function syntax is sum(iterable, start=0), where the second argument is the starting value.

2. Step 2: Identify correct argument order

   sum(nums, 10) uses sum(nums, 10), which correctly passes the iterable first and start second.

3. Final Answer:

   sum(nums, 10) -> Option A

4. Quick Check:

   sum(iterable, start) = sum(nums, 10) [OK]

Hint: Iterable first, start second in sum() [OK]

Common Mistakes:

• Swapping the order of arguments
• Using plus sign inside sum()
• Using keyword argument incorrectly

3. What is the output of the following code?

numbers = [2, 4, 6]
result = sum(numbers, 5)
print(result)

medium

A. Error

B. 12

C. 11

D. 17

Solution

1. Step 1: Calculate sum of list elements

   The list numbers contains 2, 4, and 6. Their sum is 2 + 4 + 6 = 12.

2. Step 2: Add the start value

   The start value is 5, so total is 12 + 5 = 17.

3. Final Answer:

   17 -> Option D

4. Quick Check:

   sum([2,4,6],5) = 17 [OK]

Hint: Add start value after summing list [OK]

Common Mistakes:

• Forgetting to add the start value
• Adding start value before summing
• Assuming sum returns list length

4. The code below throws an error. What is the problem?

values = [1, 2, '3', 4]
total = sum(values)

medium

A. sum() requires a start argument

B. List contains a string which cannot be added

C. sum() only works with tuples

D. Missing parentheses in sum() call

Solution

1. Step 1: Check list element types

   The list values contains integers and a string '3'. sum() cannot add strings to numbers.

2. Step 2: Understand sum() type requirements

   sum() requires all elements to be numbers. Mixing types causes a TypeError.

3. Final Answer:

   List contains a string which cannot be added -> Option B

4. Quick Check:

   sum() needs all numbers [OK]

Hint: Ensure all list items are numbers before sum() [OK]

Common Mistakes:

• Ignoring mixed data types
• Thinking sum() needs start argument
• Assuming sum() works on strings

5. You have a list of daily sales: sales = [100, 200, 0, 150, 300]. You want to calculate the total sales but ignore days with zero sales. Which code correctly uses sum() to do this?

hard

A. sum(sale for sale in sales if sale != 0)

B. sum(sales) - sales.count(0)

C. sum(sales, 0) if 0 not in sales else 0

D. sum(sales) / sales.count(0)

Solution

1. Step 1: Filter out zero sales using a generator expression

   The expression sale for sale in sales if sale != 0 creates a sequence of sales excluding zeros.

2. Step 2: Use sum() on filtered sales

   sum() adds only the non-zero sales, giving the correct total.

3. Final Answer:

   sum(sale for sale in sales if sale != 0) -> Option A

4. Quick Check:

   sum(filtered sales) = correct total [OK]

Hint: Use sum() with condition inside generator [OK]

Common Mistakes:

• Subtracting the count of zeros instead of filtering
• Using sum() with wrong condition
• Dividing sum by zero count