Convert from numbers to letters

[Mike Meyer]

Bill Mill <bill.mill at gmail.com> writes:

> On 19 May 2005 11:59:00 -0700, rh0dium <sklass at pointcircle.com> wrote:
>> This is great but backwards...
>> 
>> Ok because you all want to know why..  I need to convert Excel columns
>> A2 into , [1,0] and I need a simple way to do that..
>> 
>> ( The way this works is A->0 and 2->1 -- Yes they interchange --  So
>> B14 == [13,1] )
>
> why didn't you say this in the first place?
>
> def coord2tuple(coord):
>     row, col = '', ''
>     alpha = 'abcdefghijklmnopqrstuvwxyz'.upper()
>     pairs = [''.join((x,y)) for x in alpha for y in [''] + [z for z in alpha]]
>     pairs = sorted(pairs, key=len)
>     coord = coord.upper()
>     for c in coord:
>         if c in alpha:
>             row += c
>         else:
>             col += c
>     return (int(col)-1, pairs.index(row))

That seems like the long way around. Python can search strings for
substrings, so why not use that? That gets the search loop into C
code, where it should be faster.

from string import uppercase

def coord2tuple2(coord):
    if len(coord) > 1 or uppercase.find(coord) < 0:
       raise ValueError('coord2tuple2 expected a single uppercase character, got "%s"' % coord)
    return uppercase.index(coord) + 1

Without the initial test, it has a buglet of return values for "AB"
and similar strings. If searching uppercase twice really bothers you,
you can drop the uppercase.find; then you'll get less informative
error messages if coord2tuple2 is passed single characters that aren't
in uppercase.

    <mike
-- 
Mike Meyer <mwm at mired.org>			http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.