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Online Python

🎨 Formatting Strings

Python offers multiple ways to format strings, with f-strings being the most modern and readable approach. String formatting is essential for creating dynamic output and combining text with variables.

# Basic string formatting
name = "Alice"
age = 25
message = f"{name} is {age} years old"
print(message)

🎯 String Formatting Methods

Python provides several methods for string formatting, each with its own use cases.

F-String Examples

# F-string formatting examples
name = "Bob"
age = 30
score = 95.5

# Basic variable insertion
print(f"Name: {name}")

# Expressions
print(f"Next year's age: {age + 1}")

# Formatting numbers
print(f"Score: {score:.1f}%")

# Multiple variables
print(f"{name} is {age} years old and scored {score:.1f}%")

Format Method Examples

# Format method examples
name = "Charlie"
age = 35

# Positional arguments
print("{} is {} years old".format(name, age))

# Named arguments
print("{n} is {a} years old".format(n=name, a=age))

# Format specifiers
print("Age: {:.1f}".format(35.0))

🔍 Format Specifiers

Format specifiers control how values are displayed in formatted strings.

# Format specifier examples
number = 123.456789

# Different number formats
print(f"Default: {number}")
print(f"2 decimal places: {number:.2f}")
print(f"Scientific: {number:e}")
print(f"Percentage: {number:.1%}")

# String formatting
text = "Python"
print(f"Left aligned: {text:<10}")
print(f"Right aligned: {text:>10}")
print(f"Centered: {text:^10}")

🎨 Common Use Cases

Here are some practical examples of string formatting.

# 1. Creating a table
def print_table(data):
    for name, score in data:
        print(f"{name:<10} | {score:>5.1f}%")

# 2. Formatting currency
def format_price(amount):
    return f"${amount:,.2f}"

# 3. Creating a progress bar
def progress_bar(current, total):
    percentage = current / total * 100
    return f"[{'=' * int(percentage/10)}{' ' * (10-int(percentage/10))}] {percentage:.1f}%"

# Test the functions
scores = [("Alice", 95.5), ("Bob", 88.0), ("Charlie", 92.5)]
print_table(scores)
print(format_price(1234.56))
print(progress_bar(7, 10))

📝 Quick Practice

Let's practice string formatting with a real-world scenario!

Hands-on Exercise

Create a function to format a receipt.

python
# Receipt Formatting Practice
def format_receipt(items, tax_rate=0.1):
    # TODO: Implement receipt formatting
    # 1. Format each item with name, quantity, and price
    # 2. Calculate subtotal, tax, and total
    # 3. Format the final receipt with proper alignment
    
    # Example items: [("Apple", 2, 0.50), ("Banana", 3, 0.75)]
    return ""

# Test the function
items = [("Apple", 2, 0.50), ("Banana", 3, 0.75), ("Orange", 1, 1.25)]
print(format_receipt(items))

Solution and Explanation 💡

Click to see the solution
# Receipt Formatting Solution
def format_receipt(items, tax_rate=0.1):
    # Calculate totals
    subtotal = sum(quantity * price for _, quantity, price in items)
    tax = subtotal * tax_rate
    total = subtotal + tax
    
    # Format receipt
    receipt = "RECEIPT\n" + "=" * 30 + "\n"
    
    # Format items
    for name, quantity, price in items:
        item_total = quantity * price
        receipt += f"{name:<10} {quantity:>2} x ${price:>5.2f} = ${item_total:>6.2f}\n"
    
    # Format totals
    receipt += "-" * 30 + "\n"
    receipt += f"Subtotal: ${subtotal:>20.2f}\n"
    receipt += f"Tax: ${tax:>23.2f}\n"
    receipt += f"Total: ${total:>22.2f}\n"
    
    return receipt

# Test the function
items = [("Apple", 2, 0.50), ("Banana", 3, 0.75), ("Orange", 1, 1.25)]
print(format_receipt(items))

Key Learning Points:

  • 📌 Used f-strings with format specifiers
  • 📌 Used alignment operators (<, >, ^)
  • 📌 Used decimal formatting (.2f)
  • 📌 Used string multiplication for lines

🎯 Key Takeaways

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