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Mark Pilgrim
88 lines
3.5 KiB
Python
88 lines
3.5 KiB
Python
'''Convert to and from Roman numerals
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This program is part of 'Dive Into Python 3', a free Python book for
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experienced programmers. Visit http://diveintopython3.org/ for the
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latest version.
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'''
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import re
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class OutOfRangeError(ValueError): pass
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class NotIntegerError(ValueError): pass
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class InvalidRomanNumeralError(ValueError): pass
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roman_numeral_map = (('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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roman_numeral_pattern = re.compile('''
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^ # beginning of string
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M{0,3} # thousands - 0 to 3 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 to_roman(n):
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'''convert integer to Roman numeral'''
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if not (0 < n < 4000):
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raise OutOfRangeError('number out of range (must be 1..3999)')
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if not isinstance(n, int):
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raise NotIntegerError('non-integers can not be converted')
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result = ''
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for numeral, integer in roman_numeral_map:
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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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def from_roman(s):
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'''convert Roman numeral to integer'''
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if not roman_numeral_pattern.search(s):
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raise InvalidRomanNumeralError('Invalid Roman numeral: {0}'.format(s))
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result = 0
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index = 0
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for numeral, integer in roman_numeral_map:
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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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# Copyright (c) 2009, Mark Pilgrim, All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or without modification,
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# are permitted provided that the following conditions are met:
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#
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# * Redistributions of source code must retain the above copyright notice,
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# this list of conditions and the following disclaimer.
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# * Redistributions in binary form must reproduce the above copyright notice,
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# this list of conditions and the following disclaimer in the documentation
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# and/or other materials provided with the distribution.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 'AS IS'
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# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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# POSSIBILITY OF SUCH DAMAGE.
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