Convert spreadsheet number to column letter

Question

I\'m looking for the opposite to this Q&A: Convert an excel or spreadsheet column letter to its number in Pythonic fashion.

or this one but in python How to conv

Answer 1

Here is a recursive solution:

def column_num_to_string(n):
    n, rem = divmod(n - 1, 26)
    char = chr(65 + rem)
    if n:
        return column_num_to_string(n) + char
    else:
        return char

column_num_to_string(28)
#output: 'AB'

The inverse can also be defined recursively, in a similar way:

def column_string_to_num(s):
    n = ord(s[-1]) - 64
    if s[:-1]:
        return 26 * (column_string_to_num(s[:-1])) + n
    else:
        return n
    
column_string_to_num("AB")
#output: 28