1 """Convert to and from Roman numerals"""

     2 

     3 __author__ = "Mark Pilgrim (f8dy@diveintopython.org)"

     4 __version__ = "1.4"

     5 __date__ = "8 August 2001"

     6 __copyright__ = """Copyright (c) 2001 Mark Pilgrim

     7 

     8 This program is part of "Dive Into Python", a free Python tutorial for

     9 experienced programmers.  Visit http://diveintopython.org/ for the

    10 latest version.

    11 

    12 This program is free software; you can redistribute it and/or modify

    13 it under the terms of the Python 2.1.1 license, available at

    14 http://www.python.org/2.1.1/license.html

    15 """

    16 

    17 import re

    18 

    19 #Define exceptions

    20 class RomanError(Exception): pass

    21 class OutOfRangeError(RomanError): pass

    22 class NotIntegerError(RomanError): pass

    23 class InvalidRomanNumeralError(RomanError): pass

    24 

    25 #Define digit mapping

    26 romanNumeralMap = (('M',  1000),

    27                    ('CM', 900),

    28                    ('D',  500),

    29                    ('CD', 400),

    30                    ('C',  100),

    31                    ('XC', 90),

    32                    ('L',  50),

    33                    ('XL', 40),

    34                    ('X',  10),

    35                    ('IX', 9),

    36                    ('V',  5),

    37                    ('IV', 4),

    38                    ('I',  1))

    39 

    40 def toRoman(n):

    41     """convert integer to Roman numeral"""

    42     if not (0 < n < 5000):

    43         raise OutOfRangeError, "number out of range (must be 1..4999)"

    44     if int(n) <> n:

    45         raise NotIntegerError, "decimals can not be converted"

    46 

    47     result = ""

    48     for numeral, integer in romanNumeralMap:

    49         while n >= integer:

    50             result += numeral

    51             n -= integer

    52     return result

    53 

    54 #Define pattern to detect valid Roman numerals

    55 romanNumeralPattern = re.compile("""

    56     ^                   # beginning of string

    57     M{0,4}              # thousands - 0 to 4 M's

    58     (CM|CD|D?C{0,3})    # hundreds - 900 (CM), 400 (CD), 0-300 (0 to 3 C's),

    59                         #            or 500-800 (D, followed by 0 to 3 C's)

    60     (XC|XL|L?X{0,3})    # tens - 90 (XC), 40 (XL), 0-30 (0 to 3 X's),

    61                         #        or 50-80 (L, followed by 0 to 3 X's)

    62     (IX|IV|V?I{0,3})    # ones - 9 (IX), 4 (IV), 0-3 (0 to 3 I's),

    63                         #        or 5-8 (V, followed by 0 to 3 I's)

    64     $                   # end of string

    65     """ ,re.VERBOSE)

    66 

    67 def fromRoman(s):

    68     """convert Roman numeral to integer"""

    69     if not s:

    70         raise InvalidRomanNumeralError, 'Input can not be blank'

    71     if not romanNumeralPattern.search(s):

    72         raise InvalidRomanNumeralError, 'Invalid Roman numeral: %s' % s

    73 

    74     result = 0

    75     index = 0

    76     for numeral, integer in romanNumeralMap:

    77         while s[index:index+len(numeral)] == numeral:

    78             result += integer

    79             index += len(numeral)

    80     return result