Convert spreadsheet number to column letter

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 convert a column number (eg. 127) into an excel column (eg. AA)

def colnum_string(n):
    string = ""
    while n > 0:
        n, remainder = divmod(n - 1, 26)
        string = chr(65 + remainder) + string
    return string

print(colnum_string(28))
#output:AB

The xlsxwriter library includes a conversion function, xlsxwriter.utility.xl_col_to_name(index) and is on github

here is a working example:

>>> import xlsxwriter 
>>> xlsxwriter.utility.xl_col_to_name(10)
'K'
>>> xlsxwriter.utility.xl_col_to_name(1)
'B'
>>> xlsxwriter.utility.xl_col_to_name(0)
'A'

Notice that it's using zero-indexing.

The openpyxl library includes the conversion function (amongst others) which you are looking for, get_column_letter:

>>> from openpyxl.utils.cell import get_column_letter
>>> get_column_letter(1)
'A'
>>> get_column_letter(10)
'J'
>>> get_column_letter(3423)
'EAQ'

My recipe for this was inspired by another answer on arbitrary base conversion (https://stackoverflow.com/a/24763277/3163607)

import string

def n2a(n,b=string.ascii_uppercase):
   d, m = divmod(n,len(b))
   return n2a(d-1,b)+b[m] if d else b[m]

Example:

for i in range(23,30):
    print (i,n2a(i))

outputs

23 X
24 Y
25 Z
26 AA
27 AB
28 AC
29 AD