Warmup

Write a function big_mac that returns a dictionary with a key-value pair for each part of the big mac. It should have default parameters for cheese, onion, lettuce and tomato (booleans) so that the caller can customize their order.

print(big_mac(cheese=False))

assert big_mac(cheese=False) == {"cheese":False, "lettuce":True, "sesame_bun":True, "tomato":True}

Lesson 4.8: Unit 4 Review

Review Goals

• Make sure we understand:
  • Functions and parameters
  • Scope (local vs. global)
  • Returning values
  • Handling exceptions with try/except
  • Raising exceptions
  • Combining functions with exceptions

Warm-Up

• Quick questions:
  • What’s the difference between local and global variables?
  • Why use return instead of print in functions?
  • What happens when a ValueError is not caught?

Group Activity: Debugging

1. Work with a partner.
2. I’ll give you buggy code with errors.
3. Your task: find the error and fix it.

Example:

def add_numbers(a, b):
    return a + c   # bug: c not defined

Practice Problems

• Write a function that multiplies three numbers.
• Write a function that takes *args and returns the largest value.
• Show what happens when a local variable shadows a global one.
• Write a safe division function that handles divide-by-zero.
• Write a function that raises a ValueError if given a negative number.

Game: “Name That Error”

• I’ll show you an error message
• You guess the exception type

Problem 1

print(5 / 0)
# ?

Problem 2

nums = [1, 2, 3]
print(nums[5])
# ?

Problem 3

int("hello")
# ?

Problem 4

person = {"name": "Alex"}
print(person["age"])
# ?

Quick Check

• What keyword is used to raise an exception?
• What does a bare except: do, and why is it discouraged?
• Why should functions avoid using global variables?

Wrap-Up

• Share solutions with classmates
• Ask questions to clear up misunderstandings
• Get ready for the Lesson 4.9 quiz and the midterm coming up next