Using if statements

I am attempting to make a simple Python code that replaces numbers with roman numerals. In order to do this, I need to get the position of each number to replace it with the roman numeral equivalent. However, my code doesn't seem to work.

number = range(1,21)
number = list(number)
number = str(number)
for i in number:
    for x in i:
        if i.index(x) == 0:
            if x == "1":
                x.replace(x, "X")
            elif x == "2":
                x.replace(x, "XX")
        else:
            if x == 1:
                x.replace(x, "I")
            elif x == 2:
                x.replace(x, "II")
            elif x == 3:
                x.replace(x, "III")
            elif x == 4:
                x.replace(x, "IV")
            elif x == "5":
                x.replace(x, "V")
            elif x == "6":
                x.replace(x, "VI")
            elif x == "7":
                x.replace(x, "VII")
            elif x == "8":
                x.replace(x, "VIII")
            elif x == "9":
                x.replace(x, "IX")
            else:
                x.replace(x, "")
print number

I suspect that it has to do with the way that my if statements work, but I'm not sure. Any advice would be appreciated.