Return values in Python - Mini Project: Build & Apply

Return values

📖 Scenario: You are creating a simple calculator function that adds two numbers. This is like using a calculator to get the sum of two amounts you have in your wallet.

🎯 Goal: Build a function called add_numbers that takes two numbers and returns their sum. Then, use this function to add two numbers and print the result.

📋 What You'll Learn

Create a function named add_numbers with two parameters: a and b

Inside the function, return the sum of a and b

Call the function add_numbers with the numbers 5 and 7

Store the result in a variable called result

Print the value of result

💡 Why This Matters

🌍 Real World

Functions that return values are used everywhere, like calculating totals in shopping carts or scores in games.

💼 Career

Understanding return values is essential for writing reusable code and building programs that process and return data.

1

Create the function add_numbers

Write a function called add_numbers that takes two parameters named a and b. Inside the function, return the sum of a and b.

Python

# Define the function add_numbers with parameters a and b
# Your code here

Hint

Use the def keyword to create a function. Use return to send back the sum.

2

Call the function and store the result

Call the function add_numbers with the numbers 5 and 7. Store the returned value in a variable called result.

Python

def add_numbers(a, b):
    return a + b

# Call add_numbers with 5 and 7 and store in result
# Your code here

Hint

Use the function name with parentheses and pass the numbers inside. Assign the call to result.

3

Print the result

Write a print statement to display the value stored in the variable result.

Python

def add_numbers(a, b):
    return a + b

result = add_numbers(5, 7)

# Print the value of result
# Your code here

Hint

Use print(result) to show the sum on the screen.

4

Try with different numbers

Call the function add_numbers again with the numbers 10 and 15. Store the returned value in a variable called new_result. Then print new_result.

Python

def add_numbers(a, b):
    return a + b

result = add_numbers(5, 7)
print(result)

# Call add_numbers with 10 and 15, store in new_result, then print it
# Your code here

Hint

Repeat the call with new numbers and print the new result.

Practice

1. What does the return statement do in a Python function?

easy

A. It sends a value back to where the function was called.

B. It prints a value to the screen.

C. It creates a new variable inside the function.

D. It pauses the function without sending any value.

Solution

1. Step 1: Understand the purpose of return

   The return statement ends the function and sends a value back to the caller.

2. Step 2: Differentiate from printing or pausing

   Printing shows output but does not send a value back; pausing does not return a value.

3. Final Answer:

   It sends a value back to where the function was called. -> Option A

4. Quick Check:

   Return sends value back [OK]

Hint: Return sends value back, print shows output only [OK]

Common Mistakes:

• Confusing return with print
• Thinking return pauses without value
• Assuming return creates variables

2. Which of the following is the correct syntax to return the value 10 from a function?

easy

A. return(10,)

B. return 10

C. return = 10

D. return: 10

Solution

1. Step 1: Recall correct return syntax

   The correct syntax is simply return followed by the value without assignment or colon.

2. Step 2: Check each option

   return 10 is correct; return(10,) returns a tuple (10,) due to the trailing comma; the others cause syntax errors.

3. Final Answer:

   return 10 -> Option B

4. Quick Check:

   Return value with 'return value' syntax [OK]

Hint: Use 'return value' without assignment or colon [OK]

Common Mistakes:

• Using assignment with return
• Adding colon after return
• Using parentheses incorrectly

3. What is the output of this code?

def add(a, b):
    return a + b

result = add(3, 4)
print(result)

medium

A. None

B. 34

C. 7

D. Error

Solution

1. Step 1: Understand the function behavior

   The function add returns the sum of a and b.

2. Step 2: Calculate the return value

   Calling add(3, 4) returns 7, which is stored in result and printed.

3. Final Answer:

   7 -> Option C

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Return value is sum, printed as 7 [OK]

Common Mistakes:

• Concatenating numbers as strings
• Forgetting to return value
• Expecting print inside function

4. Find the error in this function and choose the correct fix:

def multiply(x, y):
    product = x * y
    print(product)

medium

A. Add return x, y instead of product.

B. Change print(product) to return print(product).

C. Remove product and just print x * y.

D. Add return product to send the result back.

Solution

1. Step 1: Identify the problem

   The function prints the product but does not return it, so no value is sent back.

2. Step 2: Fix by returning the product

   Adding return product sends the result back to the caller.

3. Final Answer:

   Add return product to send the result back. -> Option D

4. Quick Check:

   Return value to send result back [OK]

Hint: Return value to send it back, print only shows output [OK]

Common Mistakes:

• Returning print() instead of value
• Not returning any value
• Returning wrong variables

5. You want a function that returns the first non-empty string from a list or None if all are empty. Which function correctly does this?

hard

A. def first_non_empty(strings):
for s in strings:
if s:
return s
return None

B. def first_non_empty(strings):
for s in strings:
if s == '':
return s
return None

C. def first_non_empty(strings):
for s in strings:
if not s:
return s
return None

D. def first_non_empty(strings):
for s in strings:
return s
return None

Solution

1. Step 1: Understand the goal

   The function should return the first string that is not empty (truthy) or None if none found.

2. Step 2: Analyze each option

   The version with if not s: return s returns the first falsy (empty) string; if s == '' returns the first exactly empty string; if s: return s returns the first truthy (non-empty) string; the version without if returns the first string regardless. Only the truthy check is correct.

3. Final Answer:

   def first_non_empty(strings): for s in strings: if s: return s return None -> Option A

4. Quick Check:

   Return first truthy string or None [OK]

Hint: Return first truthy value, else None [OK]

Common Mistakes:

• Returning empty strings instead of non-empty
• Returning on first loop without condition
• Confusing truthy and falsy values