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Converts an integer between 1 and 3999 to its Roman numeral string representation.

Purpose

This function provides a mathematical conversion utility that transforms decimal integers into their Roman numeral equivalents. It uses a subtractive notation approach (e.g., IV for 4, IX for 9) and is useful for formatting numbers in classical Roman style for display purposes, document numbering, or educational applications.

Source Code

def int_to_roman(input):
   if type(input) != type(1):
      raise TypeError("expected integer, got %s" % type(input))
   if not 0 < input < 4000:
      raise ValueError("Argument must be between 1 and 3999")
   ints = (1000, 900,  500, 400, 100,  90, 50,  40, 10,  9,   5,  4,   1)
   nums = ('M',  'CM', 'D', 'CD','C', 'XC','L','XL','X','IX','V','IV','I')
   result = ""
   for i in range(len(ints)):
      count = int(input / ints[i])
      result += nums[i] * count
      input -= ints[i] * count
   return result

Parameters

Parameter Details

input: An integer value that must be between 1 and 3999 (inclusive). The function validates that the parameter is of integer type and within the valid range. Values outside this range or non-integer types will raise exceptions.

Return Value

Returns a string containing the Roman numeral representation of the input integer. The string consists of Roman numeral characters (M, D, C, L, X, V, I) and their subtractive combinations (CM, CD, XC, XL, IX, IV). For example, 1994 returns 'MCMXCIV'.

Usage Example

# Basic usage
result = int_to_roman(1994)
print(result)  # Output: 'MCMXCIV'

# More examples
print(int_to_roman(1))     # Output: 'I'
print(int_to_roman(58))    # Output: 'LVIII'
print(int_to_roman(3999))  # Output: 'MMMCMXCIX'

# Error handling
try:
    int_to_roman(4000)  # Raises ValueError
except ValueError as e:
    print(f"Error: {e}")

try:
    int_to_roman("123")  # Raises TypeError
except TypeError as e:
    print(f"Error: {e}")

Best Practices

• Always validate input is within the range 1-3999 before calling, or handle ValueError exceptions appropriately
• Ensure input is an integer type; the function will raise TypeError for other types including float
• The function modifies the input parameter internally during calculation, but this doesn't affect the caller since integers are immutable in Python
• For large-scale conversions, consider caching results if the same values are converted repeatedly
• This implementation uses standard subtractive notation (e.g., IV for 4, not IIII)

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