The Fiscal Code (Part II): the Check Letter

In this challenge, you must build a program that generates the last character of an Italian Codice Fiscale, an alphanumeric identifying ID code.

The last character, also called check letter or CIN (Control Internal Number), is calculated after converting every other character into a numeric value, in relation to the parity of their natural position into the string (treating so the string as a 1-indexed sequence).

CONVERSION TABLE

When all characters will be converted accordingly to the conversion table, you have to sum these values and divide the result by 26: the remainder will give you the index of a letter, from A = 0 up to Z = 25.

Given a string code being a partial Fiscal Code, implement a function that returns the CIN as a capitalized single letter.

Example

fiscal_code("MRTMTT25D09F205") ➞ "Z"

Convert the characters in odd positions:

Pos   Char   Value
1st  -> M -> 18
3rd  -> T -> 14
5th  -> T -> 14
7th  -> 2 -> 5
9th  -> D -> 7
11th -> 9 -> 21
13th -> 2 -> 5
15th -> 5 -> 13

Convert the characters in even positions:

Pos   Char   Value
2nd  -> R -> 17
4th  -> M -> 12
6th  -> T -> 19
8th  -> 5 -> 5
10th -> 0 -> 0
12th -> F -> 5
14th -> 0 -> 0

Sum of the values:

18 + 14 + 14 + 5 + 7 + 21 + 5 + 13 +
17 + 12 + 19 + 5 + 0 + 5 + 0 = 155

The remainder (modulo) of 155 % 26 is 25

Starting from A = 0, Z is the 25th letter

The following dict can be used for coding:

conversion_table = {
  "0": (1, 0), "I": (19, 8),
  "1": (0, 1), "J": (21, 9),
  "2": (5, 2), "K": (2, 10),
  "3": (7, 3), "L": (4, 11),
  "4": (9, 4), "M": (18, 12),
  "5": (13, 5), "N": (20, 13),
  "6": (15, 6), "O": (11, 14),
  "7": (17, 7), "P": (3, 15),
  "8": (19, 8), "Q": (6, 16),
  "9": (21, 9), "R": (8, 17),
  "A": (1, 0), "S": (12, 18),
  "B": (0, 1), "T": (14, 19),
  "C": (5, 2), "U": (16, 20),
  "D": (7, 3), "V": (10, 21),
  "E": (9, 4), "W": (22, 22),
  "F": (13, 5), "X": (25, 23),
  "G": (15, 6), "Y": (24, 24),
  "H": (17, 7), "Z": (23, 25)
}

Notes

• Remember that the positions of characters into the string are 1-indexed. On the other hand, when returning the check letter, the positions of the letters into the alphabet are 0-indexed.
• You can expect only valid data: uppercase alpha-numeric strings made of 15 valid characters.