Converting base-16 roman numbers to arabic numbers (and vice-versa)

Here is neat python programming challenge.

A hex roman numeral is very much like the standard roman numeral, except with different values. In normal roman numerals, I = 1, V = 5, X = 10 and so on. In hex roman numerals, I = 1, V = 8, X = 16, L = 128, C = 256, D = 2048 and M = 4096. So for example:

VIIII = 8 + 1 + 1 + 1 + 1 = 12
IX = 16 – 1 = 15
XV = 16 + 8 = 24
XL = 128 – 16 = 112

The goal is to write a program in python that converts it in either direction. If given a decimal number, it should return the hex roman numeral version of the number and if given a hex roman numeral, it should return the decimal version of the number.

I started this by creating a program that performs a normal roman to arabic conversion. This wasn’t too hard, especially since python has a ton of neat features such as as dictionaries and solid string parsing methods. Since I am using unittest to test my code, I’ve named this file roman_numerals.py.

The package unittest provides a great way to test your programs. I love it. You can pretty much run a another script and it will perform all the necessary assertions as it tests the proper package. Here is my unittest code, which I named test_roman_numerals.py.

Here are some screenshots of the program in action: first testing through the command line, and then testing it with unittest.


Taking this base code and making it compatible with base-16 numerals was trivial. All that I needed to do was make a minor modification to the dictionary roman_dict and adding extra elements to the lists units, tens, hundreds and thousands. Of course I had to perform a base conversion with the hex2dec function each time I wanted to access a position in the list.
Here is the code that converts base-16 roman numbers to arabic numbers. I saved this file as roman_numerals_base16.py.

And here are my test cases, taken directly from the problem statement and saved as test_roman_numerals_base16.py.

Here is a screenshot of the program in action.


Finally, if you need some python book recommendations I suggest Learning Python. That’s how I learned.