Module 4 Study Guide

Lesson 4.1: Comparison Operators

The Six Operators

Comparison operators compare two values and return a Boolean (True or False).

print(10 == 10)   # True  - equal to
print(10 != 5)    # True  - not equal to
print(5 < 10)     # True  - less than
print(10 > 5)     # True  - greater than
print(5 <= 5)     # True  - less than or equal to
print(5 >= 10)    # False - greater than or equal to

Key Points

• = assigns a value; == checks equality
• String comparison is case-sensitive: "Hello" != "hello"
• Comparing different types: "5" == 5 is False
• Integers and floats can be compared: 5 == 5.0 is True
• Results can be stored in variables: is_adult = age >= 18

Lesson 4.2: if, elif, and else

Basic Structure

# Simple if
if temperature > 30:
    print("It's hot!")

# if-else: two paths
if age >= 18:
    print("Adult")
else:
    print("Minor")

# if-elif-else: multiple paths
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
else:
    grade = "F"

Key Points

• Always end if, elif, else with a colon :
• Indent the body with 4 spaces
• In an elif chain, only the first True branch executes
• Multiple separate if statements each check independently
• else is optional and catches everything not matched above

Lesson 4.3: Logical Operators

The Three Operators

• and — True only when both sides are True
• or — True when at least one side is True
• not — Reverses: True becomes False, False becomes True

# and: both must be true
if age >= 18 and has_id:
    print("Can enter")

# or: at least one must be true
if day == "Sat" or day == "Sun":
    print("Weekend!")

# not: reverses the boolean
if not is_raining:
    print("Go outside")

Precedence and Short-Circuit

Order: not (first) → and → or (last). Use parentheses for clarity.

Short-circuit: and stops at the first False; or stops at the first True. Useful for guarding against errors (e.g., checking x != 0 before dividing by x).

Lesson 4.4: Nested Conditionals

Nesting Basics

if has_ticket:
    if age >= 18:
        print("Welcome!")
    else:
        print("Too young.")
else:
    print("Need a ticket.")

Refactoring Strategies

1. Combine with and: Replace nested ifs with if A and B:
2. Guard clauses: Check failure cases first with early returns/messages
3. Limit nesting: Keep to 3 levels or fewer

Self-Check: Can You Do This?

• Use all six comparison operators correctly
• Explain the difference between = and ==
• Write an if-elif-else chain for multiple conditions
• Explain why indentation matters in Python
• Use and, or, not to combine conditions
• Read a truth table for and and or
• Explain short-circuit evaluation with an example
• Write nested conditionals for complex decisions
• Refactor deep nesting into flatter code
• Identify and fix common conditional mistakes

Next Steps

Once you are comfortable with conditionals, you are ready for Module 5: Loops, where you will learn to repeat actions automatically using for and while loops. Conditionals and loops together form the core of programming logic!

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