letter collumn sheet letters to integer index value

sheetutils.py

#!/bin/env/python
# -*- coding: utf-8 -*-

# Author: Ricardo L. Dani
# E-mail: ricardodani@gmail.com
# Github: http://github.com/ricardodani

'''
Utility functions for spreadshett manipulation.
'''

from math import pow

def cli(c):
    '''
    Collumn letter index, returns the index number of a letter collumn
    value notation. Examples::

    >>> cli('A')
    >>> 0
    >>> cli('B')
    >>> 1
    >>> cli('C')
    >>> 2
    
    ...

    >>> cli('Z')
    >>> 25
    >>> cli('AA')
    >>> 26
    >>> cli('AB')
    >>> 27

    '''
    
    fl = ord('A') # first letter
    ll = ord('Z') # last letter
    rv = ll - fl # range value (26)
    lt = ord(c[0]) - fl # letter in recursive context
    if not (fl <= lt + fl <= ll): # validate the input
        raise Exception('Invalid input (valid only letters inside A-Z).')
    wt = len(c) -1 # weight of letter
    return pow(rv, wt) * lt + lt + c[1:] if len(c) > 1 else 0