"""Convert to and from Roman numerals""" __author__ = "Mark Pilgrim (f8dy@diveintopython.org)" __version__ = "1.4" __date__ = "8 August 2001" __copyright__ = """Copyright (c) 2001 Mark Pilgrim This program is part of "Dive Into Python", a free Python tutorial for experienced programmers. Visit http://diveintopython.org/ for the latest version. This program is free software; you can redistribute it and/or modify it under the terms of the Python 2.1.1 license, available at http://www.python.org/2.1.1/license.html """ import re #Define exceptions class RomanError(Exception): pass class OutOfRangeError(RomanError): pass class NotIntegerError(RomanError): pass class InvalidRomanNumeralError(RomanError): pass #Define digit mapping romanNumeralMap = (('M', 1000), ('CM', 900), ('D', 500), ('CD', 400), ('C', 100), ('XC', 90), ('L', 50), ('XL', 40), ('X', 10), ('IX', 9), ('V', 5), ('IV', 4), ('I', 1)) def toRoman(n): """convert integer to Roman numeral""" if not (0 < n < 5000): raise OutOfRangeError, "number out of range (must be 1..4999)" if int(n) != n: raise NotIntegerError, "decimals can not be converted" result = "" for numeral, integer in romanNumeralMap: while n >= integer: result += numeral n -= integer return result #Define pattern to detect valid Roman numerals romanNumeralPattern = re.compile(""" ^ # beginning of string M{0,4} # thousands - 0 to 4 M's (CM|CD|D?C{0,3}) # hundreds - 900 (CM), 400 (CD), 0-300 (0 to 3 C's), # or 500-800 (D, followed by 0 to 3 C's) (XC|XL|L?X{0,3}) # tens - 90 (XC), 40 (XL), 0-30 (0 to 3 X's), # or 50-80 (L, followed by 0 to 3 X's) (IX|IV|V?I{0,3}) # ones - 9 (IX), 4 (IV), 0-3 (0 to 3 I's), # or 5-8 (V, followed by 0 to 3 I's) \$ # end of string """ ,re.VERBOSE) def fromRoman(s): """convert Roman numeral to integer""" if not s: raise InvalidRomanNumeralError, 'Input can not be blank' if not romanNumeralPattern.search(s): raise InvalidRomanNumeralError, 'Invalid Roman numeral: %s' % s result = 0 index = 0 for numeral, integer in romanNumeralMap: while s[index:index+len(numeral)] == numeral: result += integer index += len(numeral) return result