Convert mutually Excel’s column names to numbers.

excel_column_name.py

# -*- coding: utf-8 -*-

import string
import re
from functools import reduce

CHARS = string.ascii_uppercase

def number_to_char(number):
    if number < 0: raise ValueError
    
    result = ''
    while number > 0:
        number, remainder = divmod(number - 1, 26)
        result = CHARS[remainder] + result
    return result

def char_to_number(char):
    if not re.match(r'^[A-Z]*$', char): raise ValueError
    return reduce(lambda sum, c: sum * 26 + CHARS.index(c) + 1, char, 0)

input = 'XFD'

number = char_to_number(input)
char = number_to_char(number)

print("Input: {0} to Number: {1} to Char: {2}".format(input, number, char))

excel_column_name.rb

# encoding: UTF-8

CHARS = ('A'..'Z').to_a

def number_to_char(number)
  raise ArgumentError if number < 1
  
  result = ''
  while number > 0
    number, remainder = (number - 1).divmod(26)
    result.prepend(CHARS[remainder])
  end
  result
end

def char_to_number(char)
  raise ArgumentError unless char =~ /^[A-Z]*$/
  char.each_char.inject(0) { |sum, c| sum * 26 + CHARS.index(c) + 1 }
end

input = 'XFD'

number = char_to_number(input)
char = number_to_char(number)

puts "Input: #{input} to Number: #{number} to Char: #{char}"