Convert roman numerals to numbers using Python

Roman Numerals are a number system used in ancient Rome. Numbers here are represented using a combination of letters. Modern style uses 7 symbols, each with different values. The largest number that can be written using these symbols are 3,999.

Symbol	Integer Value
I	1
V	5
X	10
L	50
C	100
D	500
M	1000

Numerals can be combined in different order to form numbers. See below roman numerals for numbers from 1 to 10 and some other 2 letter numerals for specific numbers.

I = 1
II = 2
III = 3
IV = 4
V = 5
VI = 6
VII = 7
VIII = 8
IX = 9
X = 10
XL = 40
XC = 90
CD = 40
CM = 900

Some other examples:
209 = CC + IX = CCIX
93 = XC + III = XCIII
1005 = M + V = MV
1045 = M + CD + V = MCDV

Convert roman numerals to integer

As seen above, we represent certain numbers using a single letter. And for some numbers, we require a combination of 2 letters. So to convert a roman numeral to integer number, the easiest way is to keep the specific values of these characters and then find the total.

Sample code below. For bigger numbers, add the specific combinations to this group. Here we are storing the values as a tuple.

def numberFromRoman(romanNum):
    valuesTuple = ( (1, 'I'), (4, 'IV'), (5, 'V'), (9, 'IX'), (10, 'X'), (40, 'XL'), (50, 'L'),
                    (90, 'XC'), (100, 'C'), (400, 'CD'), (500, 'D'), (900, 'CM'), (1000, 'M')  )
    
    nlen = len(romanNum)
    i = 0
    finalNumber = 0
    while i < nlen:
        #Check for 2 letter combination first
        if ( nlen > i+1 and any(romanNum[i:i+2] in v for v in valuesTuple) ):
            strtoCheck = romanNum[i:i+2]
            i += 2
        else:
            strtoCheck = romanNum[i:i+1]
            i += 1
        
        number = next( s[0] for s in valuesTuple if (strtoCheck == s[1]) )
        finalNumber = finalNumber + number

    print(finalNumber)

numberFromRoman('MMMCMXCIX')
numberFromRoman('MMCMXLIX')

Output: 3999 2949