Operators & String Methods

🔧 What are Operators?

In Chapter 2, you learned how to store data. Now you'll learn how to DO things with that data!

➕➖✖️➗ Arithmetic Operators - Math in Python

Arithmetic operators let you perform mathematical calculations. Python can be your super-powerful calculator!

Let's Explore Each Operator in Detail:

5 + 3.5
→ Python sees: int + float
→ Converts 5 to 5.0
→ Calculates: 5.0 + 3.5 = 8.5
→ Returns: 8.5 (a float)

17 / 5  = 3.4   (regular division - keeps decimal)
17 // 5 = 3     (floor division - removes decimal)

Think of it as: "How many COMPLETE groups can I make?"

2 ** 3 means: 2 × 2 × 2 = 8
5 ** 2 means: 5 × 5 = 25
10 ** 4 means: 10 × 10 × 10 × 10 = 10,000

Square root: 9 ** 0.5 = 3
Cube root:   27 ** (1/3) = 3

⚖️ Comparison Operators - Comparing Values

Comparison operators compare two values and return True or False. These are essential for making decisions in your programs!

x = 5   # Assignment: stores 5 in x
x == 5  # Comparison: checks if x equals 5 (returns True or False)

🧠 Logical Operators - Combining Conditions

Logical operators let you combine multiple conditions. Perfect for complex decision-making!

Condition1  Condition2  Result
True        True        True   ✓ (both true!)
True        False       False  ✗ (one is false)
False       True        False  ✗ (one is false)
False       False       False  ✗ (both false)

Condition1  Condition2  Result
True        True        True   ✓ (at least one true)
True        False       True   ✓ (at least one true)
False       True        True   ✓ (at least one true)
False       False       False  ✗ (both false)

✂️ String Methods - Manipulating Text

Strings aren't just static text - you can transform them in many ways! Python provides built-in methods (functions) that work on strings.

text = "hello"
text.upper()  # This creates "HELLO" but doesn't save it!
print(text)   # Still "hello"

# To save the change, assign it:
text = text.upper()  # Now text is "HELLO"
print(text)  # "HELLO"

🎯 F-Strings - Modern String Formatting

F-strings (formatted string literals) are the modern, easy way to put variables inside strings. They're super readable and powerful!

name = "Krishna"
age = 16
message = f"My name is {name} and I'm {age} years old"
print(message)  # My name is Krishna and I'm 16 years old

{value:.2f}   # 2 decimal places (float)
{value:,}     # Thousands separator
{value:.1%}   # Percentage with 1 decimal
{value:>10}   # Right align in 10 spaces
{value:<10}   # Left align in 10 spaces
{value:^10}   # Center in 10 spaces
{value:05}    # Pad with zeros to 5 digits

📺 Video Resources

Watch these videos to reinforce your understanding of operators and string methods:

🤖 AI Learning Prompts

Use these prompts with AI assistants to deepen your understanding. Hover over each prompt to see quick action buttons:

Understanding Operators

I'm learning about Python operators. Please help me understand:

1. What's the difference between / and // division? Give me 5 examples showing when each is useful
2. Explain the modulus operator (%) with real-world examples - why would I ever need remainders?
3. What's the difference between = and ==? This confuses me!
4. Show me the order of operations (PEMDAS) with Python examples
5. Create a mini calculator program I can build to practice all arithmetic operators

Use simple language and lots of examples!

Mastering Comparison and Logical Operators

Help me master comparison and logical operators in Python:

1. Explain each comparison operator (==, !=, >, <, >=, <=) with real-world analogies
2. What's the difference between 'and' and 'or'? Give me 5 practical examples of each
3. How does the 'not' operator work? When would I use it?
4. Show me how to combine multiple conditions (like age > 18 AND has_license)
5. Create practice problems where I need to write complex conditions
6. Common mistakes beginners make with these operators?

Explain like I'm learning this for the first time!

String Methods Deep Dive

I want to become excellent at string manipulation in Python:

1. Teach me the 10 most useful string methods with examples
2. What's the difference between .strip(), .lstrip(), and .rstrip()?
3. How do .split() and .join() work? They seem like opposites - explain!
4. Show me .replace() with multiple examples
5. What does "strings are immutable" mean? Why does it matter?
6. Create a text-processing exercise using multiple string methods

Give me lots of before/after examples!

F-String Formatting Mastery

I want to master f-strings in Python:

1. Why are f-strings better than older formatting methods?
2. Show me how to format numbers (decimals, thousands separators, percentages)
3. How do I align text with f-strings (left, right, center)?
4. Teach me how to put expressions and calculations inside f-strings
5. Show me how to create formatted tables and receipts with f-strings
6. Give me 5 practice exercises using f-strings in real scenarios

Include lots of visual examples showing the output!

✏️ Practice Exercises

Part 1: Guided Exercises

These exercises include detailed explanations to help you understand every step.

# Enhanced Calculator
num1 = 100
num2 = 7

print(f"🔢 CALCULATOR: {num1} and {num2}")
print("=" * 40)

# Basic operations
print(f"Addition:        {num1} + {num2} = {num1 + num2}")
print(f"Subtraction:     {num1} - {num2} = {num1 - num2}")
print(f"Multiplication:  {num1} × {num2} = {num1 * num2}")
print(f"Division:        {num1} / {num2} = {num1 / num2:.2f}")
print(f"Floor Division:  {num1} // {num2} = {num1 // num2}")
print(f"Modulus:         {num1} % {num2} = {num1 % num2}")

# Extra calculations
average = (num1 + num2) / 2
is_divisible = (num1 % num2 == 0)

print("=" * 40)
print(f"Average: {average:.2f}")
print(f"Is {num1} divisible by {num2}? {is_divisible}")
print(f"{num2} fits into {num1} exactly {num1 // num2} times")
print(f"with {num1 % num2} left over")

Part 2: Independent Practice

Now test your skills! Try these exercises on your own.

# Structure:
birth_year = 2007
current_year = 2024
age = current_year - birth_year
months = age * 12
days = age * 365  # Approximate

# Use f-strings to display nicely!

# Age Calculator
birth_year = 2007
current_year = 2024

# Calculations
age = current_year - birth_year
months = age * 12
days = age * 365

# Display with nice formatting
print("=" * 50)
print(f"AGE CALCULATOR")
print("=" * 50)
print(f"Birth Year:     {birth_year}")
print(f"Current Year:   {current_year}")
print("-" * 50)
print(f"You are approximately:")
print(f"  • {age} years old")
print(f"  • {months:,} months old")
print(f"  • {days:,} days old")
print("=" * 50)

# Restaurant Bill Calculator
item1 = "Pizza"
price1 = 12.99

item2 = "Pasta"
price2 = 15.50

item3 = "Salad"
price3 = 8.75

# Calculations
subtotal = price1 + price2 + price3
tax = subtotal * 0.08
tip = subtotal * 0.15
total = subtotal + tax + tip

# Formatted receipt
print("=" * 40)
print("🍽️  RESTAURANT RECEIPT")
print("=" * 40)
print(f"{item1:<30} ${price1:>6.2f}")
print(f"{item2:<30} ${price2:>6.2f}")
print(f"{item3:<30} ${price3:>6.2f}")
print("-" * 40)
print(f"{'Subtotal':<30} ${subtotal:>6.2f}")
print(f"{'Tax (8%)':<30} ${tax:>6.2f}")
print(f"{'Tip (15%)':<30} ${tip:>6.2f}")
print("=" * 40)
print(f"{'TOTAL':<30} ${total:>6.2f}")
print("=" * 40)
print("Thank you for dining with us! 😊")

# Password Strength Checker
password = "Python123"

# Check each requirement
length_ok = len(password) >= 8
has_upper = any(char.isupper() for char in password)
has_lower = any(char.islower() for char in password)
has_digit = any(char.isdigit() for char in password)

# All requirements met?
is_strong = length_ok and has_upper and has_lower and has_digit

# Display results
print("=" * 40)
print("🔒 PASSWORD STRENGTH CHECKER")
print("=" * 40)
print(f"Password: {password}")
print("-" * 40)
print(f"✓ At least 8 characters:  {length_ok}")
print(f"✓ Has uppercase letter:   {has_upper}")
print(f"✓ Has lowercase letter:   {has_lower}")
print(f"✓ Has number:             {has_digit}")
print("=" * 40)
print(f"Password is strong: {is_strong}")
print("=" * 40)

📝 Knowledge Check - Test Your Understanding!

Answer these questions to check your understanding of Chapter 3. Get instant feedback on each answer!