Roman numerals in python

gistfile1.py

#!/usr/bin/env python

# 100 = C    =  100
# 200 = CC   =  100 + 100
# 300 = CCC  =  100 + 100 + 100
# 400 = CD   = -100 + 500
# 500 = D    =  500
# 600 = DC   =  500 + 100
# 700 = DCC  =  500 + 100 + 100
# 800 = DCCC =  500 + 100 + 100 + 100
# 900 = CM   = -100 + 1000

# 2929 = MM CM XX IX = 2000 + 900 + 20 + 9

ROMAN = {
    1:    'I',
    5:    'V',
    10:   'X',
    50:   'L',
    100:  'C',
    500:  'D',
    1000: 'M',
}


# given 586, yields 6, 8, 5
def digits(num, base=10):
    while True:
        yield num % 10
        num = num // 10
        if num == 0:
            break


# given 586, yields D, L, X, X, X, V, I
def roman_digits(num):
    for index, digit in reversed(list(enumerate(digits(num)))):
        if digit < 4:  # III
            for _ in range(digit):
                yield ROMAN[10 ** index]
        elif digit == 4:  # IV
            yield ROMAN[10 ** index]
            yield ROMAN[5 * 10 ** index]
        elif digit < 9:  # VIII
            yield ROMAN[5 * 10 ** index]
            for _ in range(digit - 5):
                yield ROMAN[10 ** index]
        elif digit == 9:  # IX
            yield ROMAN[10 ** index]
            yield ROMAN[10 * 10 ** index]


def roman_numeral(num):
    return "".join(roman_digits(num))


# Test
import random
for num in range(1, 3500):
    if random.randint(0, num) < 10:
        print("%i = %s" % (num, roman_numeral(num)))