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Janto Dreijer  committed 243b76f

add roman.py

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  • Parent commits 0da80a7

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File code/roman.py

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