String index out of bounds ( Python : Dict )

[menator01]

Please use proper tags when posting.

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Here is a working example

#! /usr/bin/env python3

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

def convert(rn):
    converted = []
    for val in rn:
        if val in roman.keys():
            converted.append(roman[val])
    return sum(converted)
print(convert('XVI'))

Output:
16