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