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

This simple Python function works for columns with 1 or 2 letters.

def let(num):       

alphabeth = string.uppercase
na = len(alphabeth)

if num <= len(alphabeth):
    letters = alphabeth[num-1]
else:
    letters = alphabeth[ ((num-1) / na) - 1 ] +  alphabeth[((num-1) % na)]            

return letters

Answer 2

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

Answer 3

Just to complicate everything a little bit I added caching, so the name of the same column will be calculated only once. The solution is based on a recipe by @Alex Benfica

import string


class ColumnName(dict):
    def __init__(self):
        super(ColumnName, self).__init__()
        self.alphabet = string.uppercase
        self.alphabet_size = len(self.alphabet)

    def __missing__(self, column_number):
        ret = self[column_number] = self.get_column_name(column_number)
        return ret

    def get_column_name(self, column_number):
        if column_number <= self.alphabet_size:
            return self.alphabet[column_number - 1]
        else:
            return self.alphabet[((column_number - 1) / self.alphabet_size) - 1] + self.alphabet[((column_number - 1) % self.alphabet_size)]

Usage example:

column = ColumnName()

for cn in range(1, 40):
    print column[cn]

for cn in range(1, 50):
    print column[cn]

Answer 4

Just for people still interest in this. The chosen answer by @Marius gives wrong outputs in some cases, as commented by @jspurim. Here is the my answer.

import string
def convertToTitle(num):
    title = ''
    alist = string.uppercase
    while num:
        mod = (num-1) % 26
        num = int((num - mod) / 26)  
        title += alist[mod]
    return title[::-1]

Answer 5

Recursive one line solution w/o libraries

def column(num, res = ''):
   return column((num - 1) // 26, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'[(num - 1) % 26] + res) if num > 0 else res

Answer 6

import math

num = 3500
row_number = str(math.ceil(num / 702))
letters = ''
num = num - 702 * math.floor(num / 702)
while num:
    mod = (num - 1) % 26
    letters += chr(mod + 65)
    num = (num - 1) // 26
result = row_number + ("".join(reversed(letters)))
print(result)