🦄 Royal Treasury: Currency Validator

Difficulty: Beginner Tags: regex, validation, strings, parsing Series: CS 101: Fundamentals

Problem

The Royal Treasury needs to validate currency amounts in their ledgers. Determine if a string represents a valid currency amount.

Given a string, return True if it's a valid currency amount, False otherwise.

Valid format rules: - No currency symbols (no $, €, etc.) - No spaces - Commas for thousands separators (must be every 3 digits) - Optional decimal point with up to 2 digits - Can start with decimal point (.99) - No leading zeros (except for 0.xx)

Real-World Application

Currency validation appears in: - E-commerce platforms - validating product prices, cart totals - Banking systems - transaction amount validation - Accounting software - financial data entry - Payment gateways - processing payment amounts - Invoice systems - validating invoice line items - Expense trackers - user input validation - POS systems - price entry validation - Tax calculators - amount validation

Input

data = str  # String to validate as currency

Output

bool  # True if valid currency format, False otherwise

Constraints

• String length ≤ 100
• Only digits, commas, and decimal points
• No currency symbols or spaces

Examples

Valid Examples

• '1,234.56' - Standard format with commas and cents
• '12,345' - Thousands with comma, no decimal
• '0.10' - Ten cents
• '100' - Plain integer
• '.99' - Cents only (99 cents)
• '12,000' - Even thousands
• '1,000,000.00' - One million dollars
• '5' - Single digit

Invalid Examples

• '1,234,' - Trailing comma
• '1,23.4' - Incorrect comma placement (not every 3 digits)
• '00.5' - Leading zero
• '1,234.' - Decimal point with no digits after
• '1,' - Comma with insufficient digits
• '' - Empty string
• '$100' - Currency symbol
• '1 000' - Space instead of comma
• '1.234' - More than 2 decimal places
• '. - Just decimal point

What You'll Learn

• Regular expression patterns for validation
• Understanding grouping and alternation in regex
• Translating format specifications to regex
• Handling optional patterns
• Edge case validation

Why This Matters

Regex is a fundamental skill for: - Input validation in web forms - Data parsing and extraction - Text processing and transformation - Pattern matching at scale

Mastering regex patterns is essential for any software developer.

Starter Code

def challenge_function(data):
    """
    Validate if string represents valid currency amount.

    Args:
        data: str to validate

    Returns:
        bool: True if valid currency format, False otherwise
    """
    # Your implementation here
    pass