Conditional Statements in Python

Should your app send a discount code? Is the user old enough to create an account? Does the password match? Every meaningful program needs to make decisions, and that's exactly what conditional statements do. They're the decision-making brain of your code, allowing your programs to respond differently based on different situations. In this tutorial, you'll learn how to use if, elif, and else to build programs that think.

What Are Conditional Statements?

Conditionals are code structures that run different blocks of code based on whether a condition is true or false. Think of them as decision points in your program—like a choose-your-own-adventure book where the story branches based on your choices.

You've already learned about comparison operators (>, ==, !=) and logical operators (and, or, not) that produce True or False values. Conditionals use these boolean values to decide which code to execute.

Why Are Conditionals Essential?

Without conditionals, your programs would be completely linear—they'd execute the same code every single time, regardless of input or circumstances. Conditionals give your programs:

• Intelligence - Respond differently to different inputs
• Flexibility - Handle multiple scenarios with one program
• User interaction - Create personalized experiences
• Error handling - Deal with invalid or unexpected data

The Perfect Analogy: Traffic Lights

Think of conditionals like a traffic light system. When you approach an intersection:

• Green light → Go (first condition is True)
• Yellow light → Slow down/make a decision (second condition checked)
• Red light → Stop (default action when nothing else applies)

Your program checks each condition in order, just like you check the traffic light. Once it finds a true condition, it executes that block of code and moves on. If no conditions are true, it falls back to the "else" block—the red light that says "do this by default."

Visual Mental Model

Notice the pattern: Python checks each condition from top to bottom. The moment it finds a true condition, it executes that block and skips all the rest. If nothing is true, the else block runs as a fallback.

The Basic if Statement

The simplest conditional is a standalone if statement. It says: "If this condition is true, do something."

Example 1: Simple Age Check

# Check if user is an adult
age = 25

if age >= 18:
    print("You are an adult.")
    print("You can create a full account.")

print("Thank you for visiting!")  # This always runs

Output:

You are an adult.
You can create a full account.
Thank you for visiting!

Example 2: Conditional Discount

# Apply discount for large orders
total = 150

if total >= 100:
    print("Congratulations! You qualify for a 10% discount.")
    discount = total * 0.10
    total = total - discount
    print(f"Your new total: ${total:.2f}")

Output:

Congratulations! You qualify for a 10% discount.
Your new total: $135.00

The if-else Statement

Often, you want to do one thing if a condition is true, and something different if it's false. That's where else comes in.

Example 3: Account Type Decision

# Determine account type based on age
age = int(input("Enter your age: "))

if age >= 18:
    print("Adult account created.")
    print("Full features unlocked.")
else:
    print("Child account created.")
    print("Parental controls enabled.")

print("Welcome to our platform!")

If you enter 25:

Adult account created.
Full features unlocked.
Welcome to our platform!

If you enter 12:

Child account created.
Parental controls enabled.
Welcome to our platform!

The if-elif-else Statement

When you have more than two possibilities, use elif (short for "else if"). This lets you check multiple conditions in sequence.

Example 4: Three-Way Account System

# Create age-appropriate accounts
age = int(input("Enter your age: "))

if age >= 18:
    print("Adult account created.")
    print("All features available.")
elif age >= 13:
    print("Teen account created.")
    print("Some restrictions apply.")
else:
    print("Child account created.")
    print("Heavy parental controls active.")

print("\nAccount setup complete!")

Let's see what happens with different ages:

Age 25:

Adult account created.
All features available.

Account setup complete!

Age 15:

Teen account created.
Some restrictions apply.

Account setup complete!

Age 8:

Child account created.
Heavy parental controls active.

Account setup complete!

Multiple Conditions with Logical Operators

You can combine multiple checks in a single condition using and, or, and not.

Example 5: Login System

# Simple login validation
correct_username = "admin"
correct_password = "secret123"

username = input("Username: ")
password = input("Password: ")

if username == correct_username and password == correct_password:
    print("Welcome! Login successful.")
    print("Access granted to dashboard.")
else:
    print("Invalid credentials.")
    print("Access denied.")

Both conditions must be true for login to succeed. If either the username OR password is wrong, access is denied.

Example 6: Eligibility Checker

# Check driving eligibility
age = 17
has_license = True
has_insurance = False

if age >= 18 and has_license and has_insurance:
    print("You can drive legally.")
elif age >= 18 and has_license:
    print("You can drive but need insurance first.")
elif age >= 18:
    print("You need a license and insurance.")
else:
    print("You must be 18 or older to drive.")

Hands-On Exercise: Grade Classifier

Let's build a program that converts numerical scores to letter grades. This is a perfect exercise for practicing if-elif-else statements.

Requirements

• A (≥90): Excellent
• B (80–89): Good
• C (70–79): Satisfactory
• D (60–69): Needs Improvement
• F (<60): Failing

Step 1: Get the Score

Create a file called grade_classifier.py:

# Grade Classifier
print("=== Grade Classifier ===\n")

# Get student's score
score = int(input("Enter your score (0-100): "))

Step 2: Add the Conditional Logic

# Classify the grade
if score >= 90:
    grade = "A"
    message = "Excellent work!"
elif score >= 80:
    grade = "B"
    message = "Good job!"
elif score >= 70:
    grade = "C"
    message = "Satisfactory."
elif score >= 60:
    grade = "D"
    message = "Needs improvement."
else:
    grade = "F"
    message = "Failing. Please seek help."

Step 3: Display the Result

# Show the results
print(f"\nYour score: {score}")
print(f"Your grade: {grade}")
print(f"Comment: {message}")

Complete Code

# Grade Classifier
print("=== Grade Classifier ===\n")

# Get student's score
score = int(input("Enter your score (0-100): "))

# Classify the grade
if score >= 90:
    grade = "A"
    message = "Excellent work!"
elif score >= 80:
    grade = "B"
    message = "Good job!"
elif score >= 70:
    grade = "C"
    message = "Satisfactory."
elif score >= 60:
    grade = "D"
    message = "Needs improvement."
else:
    grade = "F"
    message = "Failing. Please seek help."

# Show the results
print(f"\nYour score: {score}")
print(f"Your grade: {grade}")
print(f"Comment: {message}")

Test Your Code

Run it with different scores:

Input: 95

=== Grade Classifier ===

Enter your score (0-100): 95

Your score: 95
Your grade: A
Comment: Excellent work!

Input: 73

=== Grade Classifier ===

Enter your score (0-100): 73

Your score: 73
Your grade: C
Comment: Satisfactory.

Common Mistakes to Avoid

# WRONG ❌
if age >= 18:
print("Adult")  # No indentation!

# CORRECT ✅
if age >= 18:
    print("Adult")  # Indented with 4 spaces

# WRONG ❌ - overlapping ranges
if score >= 60:
    grade = "D"
elif score >= 70:  # This will never run!
    grade = "C"

# CORRECT ✅ - most specific first
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
elif score >= 60:
    grade = "D"

# WRONG ❌
if password = "secret":  # This assigns, not compares!

# CORRECT ✅
if password == "secret":  # This compares

# WRONG ❌
if age >= 18
    print("Adult")

# CORRECT ✅
if age >= 18:
    print("Adult")

# WRONG ❌ - impossible condition
if age > 18 and age < 18:  # Can't be both!
    print("Teen")

# CORRECT ✅ - range check
if age >= 13 and age < 18:  # Between 13 and 17
    print("Teen")

# WRONG ❌ - too restrictive
if has_license and has_insurance:  # Must have both

# MAYBE CORRECT ✅ - depends on intent
if has_license or has_insurance:  # Has at least one

# INCOMPLETE ❌
score = int(input("Score: "))
if score >= 90:
    grade = "A"
# What if score is negative? Or > 100?

# COMPLETE ✅
score = int(input("Score: "))
if score < 0 or score > 100:
    print("Invalid score! Must be 0-100.")
elif score >= 90:
    grade = "A"
# ... rest of conditions

Mini-Project: Login Simulation

Project Goal: Build a secure login system that validates usernames and passwords.

Requirements

• Store a correct username and password
• Prompt the user for their credentials
• Check if both username AND password match
• Display appropriate success or error messages
• Bonus: Track failed login attempts and lock after 3 failures

Basic Implementation

# Simple Login System
print("=== Login System ===\n")

# Stored credentials
correct_user = "admin"
correct_pass = "secret123"

# Get user input
username = input("Username: ")
password = input("Password: ")

# Validate credentials
if username == correct_user and password == correct_pass:
    print("\n✓ Welcome! Login successful.")
    print("Access granted to dashboard.")
else:
    print("\n✗ Invalid credentials.")
    print("Access denied.")
    
    # Give specific feedback
    if username != correct_user:
        print("Hint: Username is incorrect.")
    if password != correct_pass:
        print("Hint: Password is incorrect.")

Enhanced Version with Attempt Tracking

# Login System with Attempt Tracking
print("=== Secure Login System ===\n")

# Stored credentials
correct_user = "admin"
correct_pass = "secret123"

# Track attempts
max_attempts = 3
attempts = 0

while attempts < max_attempts:
    # Get user input
    username = input("\nUsername: ")
    password = input("Password: ")
    
    # Validate credentials
    if username == correct_user and password == correct_pass:
        print("\n✓ Welcome! Login successful.")
        print("Access granted to dashboard.")
        break  # Exit the loop on success
    else:
        attempts += 1
        remaining = max_attempts - attempts
        
        print(f"\n✗ Invalid credentials.")
        
        if remaining > 0:
            print(f"You have {remaining} attempt(s) remaining.")
        else:
            print("Account locked due to too many failed attempts.")
            print("Please contact support.")

Bonus Challenges

1. Multiple users: Store multiple username/password pairs and check against all of them
2. Password strength: Check if password is at least 8 characters and contains a number
3. Case-insensitive username: Accept usernames in any case (ADMIN, admin, Admin)

Summary: Key Takeaways

You've mastered the decision-making structures in Python! Here's what you now know:

• ✅ if statements execute code only when a condition is true
• ✅ if-else statements provide two paths: one for true, one for false
• ✅ if-elif-else statements handle multiple conditions in sequence
• ✅ Logical operators (and, or, not) let you combine conditions
• ✅ Indentation is critical - it defines which code belongs to which block
• ✅ Order matters - Python checks conditions from top to bottom

What Makes Conditionals Powerful

• They give your programs intelligence - the ability to respond to different situations
• They enable user interaction - programs can adapt to user input
• They're universal - every programming language has conditionals
• They're the foundation for complex logic - most programs are built on chains of decisions

Your Next Steps

Now that you can make decisions, you're ready to repeat actions with loops. Here's your action plan:

• ✅ Complete the grade classifier and test it with different scores
• ✅ Build the login simulation with attempt tracking
• ✅ Experiment with combining multiple conditions using and/or
• ✅ Move on to the next tutorial: Loops (for and while) - where you'll learn to repeat actions efficiently