Lesson 5: Booleans & Comparisons

Course: Data Types & Variables | Duration: 2 hours | Level: Beginner

Learning Objectives

Explain what Boolean values are and why they're fundamental
Use all comparison operators correctly
Understand Python's "truthy" and "falsy" values
Combine comparisons using logical operators (and, or, not)
Use comparison chains unique to Python

Prerequisites

Lessons 1-4 of this course

Lesson Outline

Part 1: The bool Type (30 minutes)

Explanation

A Boolean (named after mathematician George Boole) has only two possible values: True or False. It's the simplest data type in Python, but it's the foundation of ALL decision-making in every program.

Every "if this happens, do that" in programming comes down to a Boolean: is this True or False?

python

# Boolean values (capital T and F!)
is_student = True
has_graduated = False
 
print(type(True))   # <class 'bool'>
print(type(False))  # <class 'bool'>
 
# Booleans are actually integers!
print(True + True)    # 2  (True == 1)
print(False + True)   # 1  (False == 0)
print(True * 10)      # 10

Comparison operators - produce Boolean results:

python

x = 10
y = 20
 
print(x == y)    # False  (equal to)
print(x != y)    # True   (not equal to)
print(x < y)     # True   (less than)
print(x > y)     # False  (greater than)
print(x <= y)    # True   (less than or equal to)
print(x >= y)    # False  (greater than or equal to)

Teacher's Note: Stress the difference between = (assignment) and == (comparison). This is the single most common beginner error when they learn if-statements in Course 3.

Examples

python

# Real-world comparisons
age = 18
salary = 50000
password = "secret123"
 
print(age >= 18)                    # True  - is adult
print(salary > 100000)              # False - is high earner
print(password == "secret123")      # True  - password correct
print(len(password) >= 8)           # True  - password long enough
 
# String comparisons (alphabetical)
print("apple" < "banana")    # True  (a comes before b)
print("Python" == "python")  # False (case sensitive!)
print("Z" > "A")             # True  (Z comes after A in ASCII)

Practice

Write 10 comparison expressions and predict whether each evaluates to True or False before running them. Test your predictions.

Part 2: Logical Operators (30 minutes)

Explanation

Logical operators combine Boolean values: and, or, not

python

# AND: both conditions must be True
print(True and True)    # True
print(True and False)   # False
print(False and True)   # False
print(False and False)  # False
 
# OR: at least one condition must be True
print(True or True)     # True
print(True or False)    # True
print(False or True)    # True
print(False or False)   # False
 
# NOT: reverses the Boolean
print(not True)    # False
print(not False)   # True

Short-circuit evaluation:

python

# AND stops at first False (doesn't evaluate rest)
# OR stops at first True (doesn't evaluate rest)
 
x = 5
print(x > 3 and x < 10)    # True  (both conditions true)
print(x < 3 and x > 0)     # False (first is False, stops there)
 
# Practical: check before dividing
denominator = 0
# Safe check - won't cause ZeroDivisionError
print(denominator != 0 and 100 / denominator > 10)   # False (stops at first False)

Python's unique comparison chaining:

python

age = 25
 
# Other languages need:
print(age >= 18 and age <= 65)   # Works
 
# Python also supports chaining:
print(18 <= age <= 65)   # Same! More readable.
print(1 < 2 < 3 < 4)    # True - all comparisons must hold
print(1 < 2 > 1.5)      # True - 2 > 1 AND 2 > 1.5

Examples

python

# Eligibility checker (without if/else - just showing Boolean results)
username = "alice_2024"
password = "SecurePass123"
age = 25
 
has_valid_username = len(username) >= 6 and username.replace("_", "").isalnum()
has_valid_password = len(password) >= 8
is_adult = age >= 18
 
can_register = has_valid_username and has_valid_password and is_adult
print(f"Can register: {can_register}")
 
# All must be True for registration

Practice

Build a password validator that checks multiple criteria and displays True/False for each:

At least 8 characters long
Contains at least one digit (use any() with comprehension - preview!)
Does not equal "password" or "123456"

Part 3: Truthy and Falsy Values (30 minutes)

Explanation

In Python, every value has a Boolean meaning when used in a conditional context. Values that act like True are called truthy, values that act like False are called falsy.

Falsy values (there are only a few):

python

# These all evaluate to False in a boolean context:
bool(False)     # False (obviously)
bool(0)         # False (zero integer)
bool(0.0)       # False (zero float)
bool("")        # False (empty string)
bool(None)      # False (None value)
bool([])        # False (empty list)
bool({})        # False (empty dict)
bool(())        # False (empty tuple)
bool(set())     # False (empty set)

Truthy values (everything else):

python

# These all evaluate to True:
bool(True)      # True
bool(1)         # True
bool(-1)        # True (any non-zero number)
bool(42)        # True
bool("hello")   # True (non-empty string)
bool(" ")       # True (space is a character!)
bool([1, 2])    # True (non-empty list)

Practical use:

python

# Instead of: if len(name) > 0:
# You can write: if name:
name = input("Enter your name: ")
if name:   # True if not empty
    print(f"Hello, {name}!")
else:
    print("No name entered")
 
# This is idiomatic Python - more readable

Examples

python

# Truthy/falsy in practice
user_input = input("Enter a value (or press Enter to skip): ")
 
# Check if user entered something
has_input = bool(user_input)
print(f"User provided input: {has_input}")
 
# Checking scores
scores = [85, 92, 78, 0, 95]
for score in scores:
    if score:   # 0 is falsy!
        print(f"Score {score} is valid")
    else:
        print(f"Score {score} - student absent or invalid")

Practice

Write a program that demonstrates 5 truthy values and 5 falsy values, using bool() to show the Boolean equivalent of each.

Part 4: Hands-on Practice (30 minutes)

Exercise 1: Voting Eligibility Checker

Build a complete voter eligibility system:

python

# Get inputs
name = input("Full name: ")
age = int(input("Age: "))
is_citizen = input("Are you a citizen? (yes/no): ").lower() == "yes"
is_registered = input("Are you registered? (yes/no): ").lower() == "yes"
 
# Evaluate eligibility
is_old_enough = age >= 18
can_vote = is_old_enough and is_citizen and is_registered
 
# Display results
print(f"\nEligibility Report for {name}:")
print(f"  Age requirement (18+): {is_old_enough}")
print(f"  Citizenship:           {is_citizen}")
print(f"  Registration:          {is_registered}")
print(f"  CAN VOTE:              {can_vote}")

Given product data (name, price, in_stock), create Boolean expressions to filter:

Products under $50
Products in stock
Products in stock AND under $50
Products out of stock OR over $100 (clearance candidates)

Bonus Challenge

Logic gate simulator: Implement AND, OR, XOR, NAND, NOR gates using Python's Boolean operators. Display truth tables for each.

Key Takeaways

bool has two values: True and False (capitalize!)
Comparison operators: ==, !=, <, >, <=, >=
Logical operators: and (both true), or (either true), not (reverse)
Python comparison chaining: 18 <= age <= 65 (unique to Python)
Falsy: False, 0, 0.0, "", None, [], {}, ()
Everything else is truthy
bool(value) converts any value to True/False

Common Mistakes to Avoid

= vs ==: age = 18 (assignment), age == 18 (comparison returning True/False)
Case sensitivity: True and False must be capitalized (not true, TRUE, false)
Assuming " " is falsy: a space character is truthy - only empty string "" is falsy

Homework

Build a "loan qualifier" that evaluates 5 criteria (income, credit score, employment years, debt ratio, down payment) and shows which criteria are met
Experiment with comparison chains: what does 1 < 2 < 3 < 4 < 5 return?
Research: What is "De Morgan's law" and how does it apply to Python and/or/not?

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Lesson 5: Booleans & Comparisons

Learning Objectives

Prerequisites

Lesson Outline

Part 1: The bool Type (30 minutes)

Explanation

Examples

Practice

Part 2: Logical Operators (30 minutes)

Explanation

Examples

Practice

Part 3: Truthy and Falsy Values (30 minutes)

Explanation

Examples

Practice

Part 4: Hands-on Practice (30 minutes)

Exercise 1: Voting Eligibility Checker

Exercise 2: Product Filter

Bonus Challenge

Key Takeaways

Common Mistakes to Avoid

Homework

Concept Map

Practice Exercises