Integer to Roman

#!/usr/bin/env python
# coding=utf-8
def int2roman(num):
    ret=""
    while num > 0 :
        if num >= 1000:
            ret += "M" * (num /1000)
            num = num % 1000
        elif num >= 100:
            n3 = num/100
            if n3 == 9:
                ret+="CM"
            elif n3>= 5:
                ret += "D"
                n3 -= 5
                ret += n3 * "C"
            elif n3 == 4:
                ret += "CD"
            else:
                ret += n3 * "C"
            num = num % 100
        elif num >= 10:
            n2 = num /10
            if n2 == 9:
                ret += "XC"
            elif n2 >=5:
                ret += "L"
                n2 -=5
                ret += n2 * "X"
            elif n2 == 4:
                ret += "XL"
            else:
                ret += n2 * "X"
            num = num %10
        elif num > 0:
            if num == 9:
                ret += "IX"
            elif num >=5:
                ret += "V"
                num -= 5
                ret += num * "I"
            elif num == 4:
                ret += "IV"
            else:
                ret += num * "I"
            num = 0
            
    #print(ret)
    return ret


int2roman(18)
int2roman(19)
int2roman(1666)
int2roman(1888)
int2roman(1984)
int2roman(2000)
int2roman(3999)