Basic program to convert integer to Roman numerals?

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One of the best ways to deal with this is using the divmod function. You check if the given number matches any Roman numeral from the highest to the lowest. At every match, you should return the respective character.

Some numbers will have remainders when you use the modulo function, so you also apply the same logic to the remainder. Obviously, I’m hinting at recursion.

See my answer below. I use an OrderedDict to make sure that I can iterate “downwards” the list, then I use a recursion of divmod to generate matches. Finally, I join all generated answers to produce a string.

from collections import OrderedDict

def write_roman(num):

    roman = OrderedDict()
    roman[1000] = "M"
    roman[900] = "CM"
    roman[500] = "D"
    roman[400] = "CD"
    roman[100] = "C"
    roman[90] = "XC"
    roman[50] = "L"
    roman[40] = "XL"
    roman[10] = "X"
    roman[9] = "IX"
    roman[5] = "V"
    roman[4] = "IV"
    roman[1] = "I"

    def roman_num(num):
        for r in roman.keys():
            x, y = divmod(num, r)
            yield roman[r] * x
            num -= (r * x)
            if num <= 0:
                break

    return "".join([a for a in roman_num(num)])

Taking it for a spin:

num = 35
print write_roman(num)
# XXXV

num = 994
print write_roman(num)
# CMXCIV

num = 1995
print write_roman(num)
# MCMXCV

num = 2015
print write_roman(num)
# MMXV

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