Convert an excel or spreadsheet column letter to its number in Pythonic fashion

Question

Is there a more pythonic way of converting excel-style columns to numbers (starting with 1)?

Working code up to two letters:

Answer 1

Here is one way to do it. It is a variation on code in the XlsxWriter module:

def col_to_num(col_str):
    """ Convert base26 column string to number. """
    expn = 0
    col_num = 0
    for char in reversed(col_str):
        col_num += (ord(char) - ord('A') + 1) * (26 ** expn)
        expn += 1

    return col_num


>>> col_to_num('A')
1
>>> col_to_num('AB')
28
>>> col_to_num('ABA')
729
>>> col_to_num('AAB')
704