trying to match a string

[oj]

On Jul 18, 12:10 pm, John Machin <sjmac... at lexicon.net> wrote:
> On Jul 18, 9:05 pm, oj <ojee... at gmail.com> wrote:
>
>
>
> > On Jul 18, 11:33 am, arnimavidyar... at gmail.com wrote:
>
> > > Hi,
>
> > > Hi,
>
> > > I am taking a string as an input from the user and it should only
> > > contain the chars:L , M or R
>
> > > I tried the folllowing in kodos but they are still not perfect:
>
> > > [^A-K,^N-Q,^S-Z,^0-9]
> > > [L][M][R]
> > > [LRM]?L?[LRM]? etc but they do not exactly meet what I need.
>
> > > For eg: LRLRLRLRLM is ok but LRLRLRNL is not as it has 'N' .like that.
>
> > > regards,
> > > SZ
>
> > > The string may or may not have all the three chars.
>
> > With regular expressions, [^LRM] matches a character that isn't L, R
> > or M. So:
>
> > import re
>
> > var = "LRLRLRLNR"
>
> > if re.search(r'[^LRM]', var):
> >     print "Invalid"
>
> Fails if var refers to the empty string.

No it doesn't, it succeeds if var is an empty string. An empty string
doesn't contain characters that are not L, R or M.

The OP doesn't specify whether an empty string is valid or not. My
interpretation was that an empty string would be valid.