Python Conditional Statements: Comparison Operators and Control Flow

Conditional statements allow your Python programs to make decisions. In this guide, you’ll learn how to use if, elif, and else with comparison operators to control program flow. Includes examples and practice exercises.

Comparison Operators

These operators return True or False to evaluate conditions:

• == : Equal to
• != : Not equal to
• > : Greater than
• < : Less than
• >= : Greater than or equal to
• <= : Less than or equal to

# Example: Check if a number is positive
num = 10
if num > 0:
    print("Positive number")

Conditional Statements (if, elif, else)

Basic if Statement

disk_usage = 85
if disk_usage > 80:
    print("Warning: Disk usage is above 80%")

if-elif-else Chain

status_code = 404
if status_code == 200:
    print("OK")
elif status_code == 404:
    print("Not found")
else:
    print("Error")

Nested Conditionals

user_logged_in = True
user_role = 'admin'

if user_logged_in:
    if user_role == 'admin':
        print("Access granted to admin panel")
else:
    print("Login required")

Even/Odd Check

number = int(input("Enter a number: "))
if number % 2 == 0:
    print(f"{number} is even")
else:
    print(f"{number} is odd")

Practice Work

Exercise 1: Fix the Code

Identify and correct errors in this conditional statement:

temperature = 32
if temperature =< 0: print("Freezing") elif temperature > 0 or temperature < 30:
    print("Cold")
eles:
    print("Hot")

temperature = 32
if temperature <= 0:
    print("Freezing")
elif 0 < temperature < 30:
    print("Cold")
else:
    print("Hot")

Exercise 2: User Authentication

Write a program that checks if:

• Username is “admin”
• Password is “secret123”

# Your code here
username = input("Enter username: ")
password = input("Enter password: ")

if username == "admin" and password == "secret123":
    print("Access granted")
else:
    print("Invalid credentials")

Exercise 3: Grade Classifier

Convert a numerical score (0-100) to a letter grade:

• A: 90-100
• B: 80-89
• C: 70-79
• F: Below 70

score = 85
if score >= 90:
    print("A")
elif score >= 80:
    print("B")
elif score >= 70:
    print("C")
else:
    print("F")

Workshop: Real-World Scenarios

Workshop 1: Discount Calculator

Apply discounts based on purchase amount:

• $100+ : 10% off
• $200+ : 20% off
• $500+ : 30% off

amount = float(input("Enter purchase amount: $"))
# Your code here

Workshop 2: Leap Year Checker

A year is a leap year if:

• Divisible by 4, but not by 100
• Unless also divisible by 400

year = 2024
# Your code here

Best Practices

• Avoid Deep Nesting: Use elif instead of multiple nested if statements.
• Use Parentheses for Complex Conditions: (x > 5) and (y < 10)
• Write Readable Conditions: Use variables like is_logged_in instead of user == True.

Conclusion

Conditional statements are the backbone of decision-making in Python. Master comparison operators and practice with real-world scenarios to write efficient, readable code.

Next: Explore Python Loops and Logical Operators.