p089.py

"""The rules for writing Roman numerals allow for many ways of writing
each number (see About Roman Numerals...). However, there is always a
"best" way of writing a particular number.

For example, the following represent all of the legitimate ways of
writing the number sixteen:

IIIIIIIIIIIIIIII
VIIIIIIIIIII
VVIIIIII
XIIIIII
VVVI
XVI

The last example being considered the most efficient, as it uses the
least number of numerals.

The 11K text file, roman.txt (right click and 'Save Link/Target
As...'), contains one thousand numbers written in valid, but not
necessarily minimal, Roman numerals; that is, they are arranged in
descending units and obey the subtractive pair rule (see About Roman
Numerals... for the definitive rules for this problem).

Find the number of characters saved by writing each of these in their
minimal form.

Note: You can  assume that all the Roman numerals  in the file contain
no more than four consecutive identical units.

"""

def abreviate(rom):
    return (rom.replace("DCCCC", "CM")
            .replace("CCCC", "CD")
            .replace("LXXXX", "XM")
            .replace("XXXX", "XL")
            .replace("VIIII", "IM")
            .replace("IIII", "IV"))

ans = sum(len(rom) - len(abreviate(rom)) for rom in open("p089.txt"))

print(ans)