Guido van Rossum | af554a0 | 2007-08-16 23:48:43 +0000 | [diff] [blame^] | 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 |