Methods with return values in Python - Mini Project: Build & Apply

Methods with return values

📖 Scenario: You are creating a simple calculator program that can add two numbers and return the result.

🎯 Goal: Build a method that takes two numbers, adds them, and returns the sum. Then use this method to get the result and print it.

📋 What You'll Learn

Create a method named add_numbers that takes two parameters: a and b.

The method add_numbers should return the sum of a and b.

Call the method add_numbers with two numbers and store the result in a variable named result.

Print the value of result.

💡 Why This Matters

🌍 Real World

Methods that return values are used in calculators, games, and many apps to perform tasks and give back results.

💼 Career

Understanding how to write and use methods with return values is a key skill for software developers to create reusable and organized code.

1

Create two number variables

Create two variables called num1 and num2 and set them to 5 and 7 respectively.

Python

# Create variables num1 and num2 with values 5 and 7
# Your code here

Hint

Use = to assign values to variables.

2

Define the add_numbers method

Define a method named add_numbers that takes two parameters called a and b. The method should return the sum of a and b.

Python

num1 = 5
num2 = 7

# Define the add_numbers method below
# Your code here

Hint

Use def to define a method and return to send back the result.

3

Call the add_numbers method and store the result

Call the method add_numbers with num1 and num2 as arguments. Store the returned value in a variable called result.

Python

num1 = 5
num2 = 7

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

# Call add_numbers with num1 and num2 and store in result
# Your code here

Hint

Call the method by writing its name and passing the variables inside parentheses.

4

Print the result

Print the value of the variable result to display the sum of the two numbers.

Python

num1 = 5
num2 = 7

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

result = add_numbers(num1, num2)

# Print the result
# Your code here

Hint

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

Practice

1. What does a method with a return statement do in Python?

easy

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

B. It prints a value on the screen.

C. It stops the program immediately.

D. It creates a new variable automatically.

Solution

1. Step 1: Understand the purpose of return

   The return statement sends a value back from the method to the caller.

2. Step 2: Differentiate from printing or stopping

   Printing shows output but does not send a value back; stopping ends execution.

3. Final Answer:

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

4. Quick Check:

   Method return = sends value back [OK]

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

Common Mistakes:

• Confusing return with print
• Thinking return stops the program
• Believing return creates variables

2. Which of the following is the correct syntax for a method that returns the sum of two numbers a and b?

easy

A. def add(a, b): return a - b

B. def add(a, b): print(a + b)

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

D. def add(a, b): a + b

Solution

1. Step 1: Identify correct return usage

   The method must use return to send back the sum a + b.

2. Step 2: Check each option

   The version with return a - b returns the difference. The version with print(a + b) prints but returns None. The version with just a + b lacks return. Only def add(a, b): return a + b correctly returns the sum.

3. Final Answer:

   def add(a, b): return a + b -> Option C

4. Quick Check:

   Return sum = def add(a, b): return a + b [OK]

Hint: Return must be followed by value to send back [OK]

Common Mistakes:

• Using print instead of return
• Omitting return keyword
• Returning wrong expression

3. What is the output of this code?

def multiply(x, y):
    return x * y

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

medium

A. 7

B. 12

C. 34

D. None

Solution

1. Step 1: Understand the method call

   The method multiply returns the product of 3 and 4, which is 12.

2. Step 2: Print the returned value

   The variable result stores 12, so print(result) outputs 12.

3. Final Answer:

   12 -> Option B

4. Quick Check:

   3 * 4 = 12 [OK]

Hint: Multiply inputs, return result, print shows it [OK]

Common Mistakes:

• Adding instead of multiplying
• Printing None by missing return
• Confusing string concatenation with multiplication

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

def greet(name):
    print("Hello, " + name)

message = greet("Alice")
print(message)

medium

A. Remove the argument name from the method.

B. Add print before calling greet.

C. Change message to greet in the last print.

D. Change print to return inside the method.

Solution

1. Step 1: Identify the problem with return value

   The method prints but does not return a value, so message is None.

2. Step 2: Fix by returning the greeting string

   Replace print with return to send the greeting back.

3. Final Answer:

   Change print to return inside the method. -> Option D

4. Quick Check:

   Return greeting to assign message [OK]

Hint: Use return to get value, not print [OK]

Common Mistakes:

• Expecting print to return a value
• Removing needed parameters
• Changing variable names incorrectly

5. You want to write a method that returns a dictionary with keys as numbers from 1 to n and values as their squares. Which method below correctly does this?

hard

A. def squares(n):
result = {}
for i in range(1, n+1):
result[i] = i * i
return result

B. def squares(n):
result = []
for i in range(n):
result.append(i * i)
return result

C. def squares(n):
return {i: i + i for i in range(1, n)}

D. def squares(n):
for i in range(1, n+1):
print(i * i)

Solution

1. Step 1: Understand the requirement

   The method must return a dictionary with keys 1 to n and values as squares.

2. Step 2: Check each option

   The loop building result = {}, setting result[i] = i * i for i in range(1, n+1), and returning result is correct. Returning a list fails. The comprehension {i: i + i for i in range(1, n)} uses doubles instead of squares and misses key n. Printing without returning fails.

3. Final Answer:

   def squares(n): result = {} for i in range(1, n+1): result[i] = i * i return result -> Option A

4. Quick Check:

   Return dict with squares = def squares(n): result = {} for i in range(1, n+1): result[i] = i * i return result [OK]

Hint: Return dict with keys and squares using loop [OK]

Common Mistakes:

• Returning list instead of dict
• Using wrong range limits
• Printing instead of returning