[Python-Dev] string.find() again (was Re: timsort for jython)

[Tim Peters]

> Tim>     re1 in re2
>
> Tim> should be True iff the language accepted by re1 is a subset of
> Tim> the language accepted by re2.  In this case, it's OK to consider
> Tim> the empty language a subset of all others, since nobody will be
> Tim> able to make head or tail out of the code anyway.

[ark@research.att.com]
> Note the distinction between the empty language and the empty string.
> As a language is a set of strings, the empty language is one that
> contains no strings, not even the empty string.  Therefore, a regular
> expression that accepts the empty language is one that rejects every
> string, even the empty string.

Sure, that's why I said "empty language" and not "empty string".  It
wouldn't make *any* sense for "re1 in re2" to consider a regexp that
accepted the language {""} to be "in" all other regexps.  But a regexp that
accepts the language {} (i.e., the empty language) clearly accepts a subset
of the language accepted by any regexp.

> Pedantically y'rs    --ark

Not enough to matter in this case <wink>.