roman numerals tdd fridays

roman_numerals.py

order = ['I', 'V', 'X', 'L', 'C', 'D', 'M']

equivalences = {
    'IIIII': 'V',
    'VV': 'X',
    'XXXXX': 'L',
    'LL': 'C',
    'CCCCC': 'D',
    'DD': 'M',
}

short_forms = {
    'IIII': 'IV',
    'VIIII': 'IX',
    'XXXX': 'XL',
    'LXXXX': 'XC',
    'DCCCC': 'CM',
}


def short_to_long(numeral):
    for long, short in short_forms.items():
        numeral = numeral.replace(short, long)
    return numeral


def long_to_short(numeral):
    for long, short in reversed(list(short_forms.items())):
        numeral = numeral.replace(long, short)
    return numeral


def add(first, second):
    first = short_to_long(first)
    second = short_to_long(second)

    result = ''.join(sorted(
        first + second,
        key=lambda x: order.index(x),
        reverse=True
    ))

    for long, short in equivalences.items():
        result = result.replace(long, short)

    return long_to_short(result)

test_roman_numerals.py

from roman_numerals import add
import pytest


@pytest.mark.parametrize('first,second,expected', [
    ('I', 'I', 'II'),
    ('I', 'II', 'III'),
    ('II', 'III', 'V'),
    ('V', 'I', 'VI'),
    ('I', 'V', 'VI'),
    ('V', 'V', 'X'),
    ('VII', 'III', 'X'),
    ('III', 'VII', 'X'),
    ('XXVII', 'III', 'XXX'),
    ('XXX', 'XX', 'L'),
    ('XXXV', 'XV', 'L'),
    ('XV', 'XXXV', 'L'),
    ('L', 'L', 'C'),
    ('LXXX', 'XX', 'C'),
    ('XX', 'LXXX', 'C'),
    ('C', 'I', 'CI'),
    ('L', 'I', 'LI'),
    ('L', 'X', 'LX'),
    ('X', 'I', 'XI'),
    ('X', 'V', 'XV'),
    ('CCC', 'CC', 'D'),
    ('D', 'D', 'M'),
    ('M', 'D', 'MD'),

])
def test_non_backwards_ones(first, second, expected):
    assert add(first, second) == expected


@pytest.mark.parametrize('first,second,expected', [
    ('IV', 'I', 'V'),
    ('I', 'IV', 'V'),
    ('IV', 'IV', 'VIII'),
    ('XIV', 'I', 'XV'),
    ('IX', 'I', 'X'),
    ('I', 'IX', 'X'),
    ('XL', 'X', 'L'),
    ('X', 'XL', 'L'),
    ('II', 'II', 'IV'),
    ('XX', 'XX', 'XL'),
    ('VIII', 'I', 'IX'),
    ('LXXX', 'X', 'XC'),
    ('XLIV', 'I', 'XLV'),
    ('IX', 'I', 'X'),
    ('MDCCCXCV', 'CIV', 'MCMXCIX')

])
def test_backwards_ones(first, second, expected):
    assert add(first, second) == expected