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somya_agrawal   1.288
ajneufeld       0.737
jg              1.521
jg2             1.324

somya_agrawal   1.288
ajneufeld       0.737
jg              1.521
jg2             1.324
maarten_bodewes 2.186
maarten_bodewes 1.653 (decode only)

With 3999 as the maximum, the longest Roman numeral string would be 12 characters ("MMMCCCXXXIII"). Your last loop would iterate 11 times, taking two letter substrings.

With 3999 as the maximum, the longest Roman numeral string would be 15 characters ("MMMDCCCLXXXVIII"). Your last loop would iterate 14 times, taking two letter substrings.

CHECKS = {"IV": 2, "IX": 2, "XL": 20, "XC": 20, "CD": 200, "CM": 200}
VALUES = {"I": 1, "V": 5, "X":10, "L": 50, "C": 100, "D": 500, "M": 1000}

def roman_to_int(roman: str) -> int:
   
    number = sum(VALUES[ch] for ch in roman)
    number -= sum(val for key, val in CHECKS.items() if key in roman)

    return number

Although I'm not a fan of CHECKS, but a better concise name is escaping me.

SUBTRACTIVE = {"IV": 2, "IX": 2, "XL": 20, "XC": 20, "CD": 200, "CM": 200}
VALUES = {"I": 1, "V": 5, "X":10, "L": 50, "C": 100, "D": 500, "M": 1000}

def roman_to_int(roman: str) -> int:
   
    number = sum(VALUES[ch] for ch in roman)
    number -= sum(val for key, val in SUBTRACTIVE.items() if key in roman)

    return number

Although I'm not a fan of CHECKS, but a better concise name is escaping me. Now using SUBTRACTIVE as suggested by JollyJoker.