"""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