Quiz: Functions — Writing Reusable Code

Test your understanding before moving on. Target: 70% or higher to proceed confidently.

Section 1: Multiple Choice (1 point each)

1. What keyword is used to define a function in Python?

• A) function
• B) def
• C) fn
• D) define

2. What is the difference between a parameter and an argument?

• A) They are the same thing — different words for the same concept
• B) A parameter is the variable in the function definition; an argument is the value passed when calling
• C) A parameter is for input; an argument is for output
• D) Parameters are required; arguments are optional

3. What does this function return?

def mystery(x):
    x = x * 2
    print(x)

• A) The doubled value of x
• B) None
• C) The original value of x
• D) An error

4. What is the output of this code?

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

result = add(3, 4)
print(result)
print(add(10, 20))

• A) 7 and 30 on separate lines
• B) 7 only
• C) 30 only
• D) Nothing — functions only compute, they don't display

5. Which of the following is a valid function definition with a default parameter?

• A) def greet(greeting="Hello", name):
• B) def greet(name, greeting="Hello"):
• C) def greet(name="Alice", greeting="Hello"):
• D) Both B and C

6. What does *args do in a function definition?

• A) Makes all arguments required
• B) Collects extra positional arguments into a tuple
• C) Collects extra keyword arguments into a dictionary
• D) Multiplies the arguments together

7. What is the output?

x = 5

def change():
    x = 10

change()
print(x)

• A) 5
• B) 10
• C) None
• D) NameError

8. Which error will this code produce?

total = 100

def update_total():
    total = total + 50
    return total

update_total()

• A) SyntaxError
• B) TypeError
• C) UnboundLocalError
• D) No error — it works fine

9. What is the LEGB rule?

• A) A coding style guideline
• B) Python's variable lookup order: Local, Enclosing, Global, Built-in
• C) A function naming convention
• D) The order in which Python executes function calls

10. What is the purpose of a docstring?

• A) To make the function run faster
• B) To document what a function does, accessible via help()
• C) To test the function automatically
• D) To prevent the function from being modified

Section 2: True/False with Justification (1 point each)

11. "A function must always have at least one parameter."

12. "Using print() inside a function is the same as using return."

13. "If you define a variable inside a function, it can be accessed outside the function."

14. "A function that doesn't have a return statement returns None."

Section 3: Short Answer (2 points each)

15. Explain why this code is dangerous and show how to fix it:

def add_student(name, roster=[]):
    roster.append(name)
    return roster

def add_student(name, roster=None):
    if roster is None:
        roster = []
    roster.append(name)
    return roster

16. Consider this call stack snapshot:

| validate_input(user_input="abc")     |  <-- top
| process_form(data={...})             |
| handle_request(request=<Request>)    |
| main()                               |
|______________________________________|

Which function is currently executing? If validate_input raises an error, in what order will Python report the functions in the traceback? Why is this order useful for debugging?

17. Why is this considered bad function design, and how would you improve it?

def process(d, n, t):
    r = d * n
    tax = r * t
    return r + tax

def calculate_total_with_tax(price, quantity, tax_rate):
    """Calculate the total cost including tax.

    Parameters:
        price (float): Unit price of the item.
        quantity (int): Number of items.
        tax_rate (float): Tax rate as a decimal (e.g., 0.08 for 8%).

    Returns:
        float: Total cost including tax.
    """
    subtotal = price * quantity
    tax = subtotal * tax_rate
    return subtotal + tax

Section 4: Code Analysis and Tracing (3 points each)

18. Trace through this code and write the exact output. Show your work by tracking variable values at each step:

def double(n):
    return n * 2

def add_one(n):
    return n + 1

def transform(value):
    step1 = double(value)
    step2 = add_one(step1)
    return step2

result = transform(5)
print(result)
print(double(add_one(3)))

11
8

19. Predict the output of this code and explain why:

def outer():
    result = []

    def add_greeting(name):
        result.append(f"Hello, {name}!")

    add_greeting("Alice")
    add_greeting("Bob")
    return result

greetings = outer()
print(greetings)
print(len(greetings))

['Hello, Alice!', 'Hello, Bob!']
2

20. What is wrong with this function, and what will happen when it is called?

def factorial(n):
    result = 1
    for i in range(1, n + 1):
        result *= i
    print(f"{n}! = {result}")

answer = factorial(5)
next_step = answer + 1

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