A roman numeral converter - http://dalelane.co.uk/blog/?p=3244

graceparse.py

# Converting roman numerals into numbers
#
#   A homework helper by Dale and Grace Lane
#          1-Nov-2014
#   
#    http://dalelane.co.uk/blog/?p=3244


#
# some simple helper functions to make 
#  the main code more readable
#

def thereAreLettersLeft(letterPosition, numberOfLetters):
	return letterPosition < numberOfLetters

def convertLetterToNumber(letter):
	romannumerals = {
		'I' : 1,
		'V' : 5, 
		'X' : 10, 
		'L' : 50, 
		'C' : 100,
		'D' : 500,
		'M' : 1000
	}
	return romannumerals[letter]

def thisIsTheLastLetter(letterPosition, lastLetterPosition):
	return letterPosition == lastLetterPosition

def addToTotal(toAdd, total):
	return toAdd + total



#
# the main roman numeral parser
#


# get the user to type in some roman numerals
romannumber = raw_input("Enter a number in roman numerals: ")

# break up the word into separate letters
letters = list(romannumber)

numberOfLetters  = len(letters)
firstLetterPosition = 0
lastLetterPosition = (numberOfLetters - 1)

# adding up the total as we go - start at 0
total = 0


# start at the beginning
letterPosition = firstLetterPosition

while thereAreLettersLeft(letterPosition, numberOfLetters):
	# look at the first letter
	firstletter = letters[letterPosition]
	# work out what it is
	firstnumber = convertLetterToNumber(firstletter)

	if thisIsTheLastLetter(letterPosition, lastLetterPosition):
		# this is the last letter - just add the
		#  value on and then we're finished
		total = addToTotal(firstnumber, total)
	else:
		# there is another letter after this - we need to 
		#  peek at it to decide what to do next

		# look at the next letter
		nextletter = letters[letterPosition + 1]
		# work out what it is
		nextnumber = convertLetterToNumber(nextletter)

		if nextnumber > firstnumber:
			# next letter is bigger, so we have to 
			#  subtract this from it
			total = addToTotal((nextnumber - firstnumber), total)

			# we've used the next letter, so skip over it
			letterPosition = letterPosition + 1
		else:
			# this letter is bigger so add the value
			total = addToTotal(firstnumber, total)

	# move on to the next letter
	letterPosition = letterPosition + 1


# finished - show our answer
print romannumber + " = " + str(total)