[Python] How to type annotate length of string?

I want to type annotate a function that only accepts a single character in python, take this example: (s: str) -> int

As Python doesn't have a type for a single char, you can't just do something like (s: char) -> int.

Is there any way to type that the s: str should only be one character?

I could see this being useful in hinting when writing code.

Here's my full example:

import unicodedata

roman_numeral_lookup = {"I": 1, "V": 5, "X": 10, ...}

def exact_roman_numeral(s: str) -> int:
"""Return the value of a single Roman numeral. Dosen't support multicharacter roman numerals such as 'XII' or Apostrophus."""

# Convert Unicode Roman numerals into to their normalised text version. e.g. Ⅹ -> X, ⅰ -> I
s = unicodedata.normalize("NFKC", s).upper()

if s in roman_numeral_lookup:
return roman_numeral_lookup

else: # Some form of invalid value.
if not isinstance(s, str):
raise TypeError("Argument must be of type str.")
elif len(s) != 1:
raise ValueError("Must be a single Roman numeral.")
else:
raise ValueError("Not a valid/supported Roman numeral.")


(I know the errors aren't the best)

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