extras/roman.py

   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
  81