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

Guido van Rossum guido@python.org
Tue, 06 Aug 2002 07:44:17 -0400

> On 5 Aug 2002 at 16:50, Gordon McMillan wrote:
> > What I'm really saying is that I almost never use x
> > in str because it's semantics have always been
> > peculiar. Thus, I don't *really* care whether '' in
> > str raises an exception, because if it does, I
> > won't train myself to use it <wink>. 
> Turns out that's not true. When I want set membership,
> I first write "char in ('a', 'b', 'c')", then
> sometimes change it because "char in 'abc'" is more
> efficient.
> So whether '' in 'abc' will work or not is a red
> herring. The real issue is that membership gets
> conflated with subsetting.

Well, in current Python you can only safely make that transformation
when you're damn sure that char is a string of length one, otherwise
you'd risk a TypeError.  So this code (if correct) will continue to
work, assuming you're not cathing TypeError (which is often an
assumption when we say that a new feature "won't break old code").

--Guido van Rossum (home page: http://www.python.org/~guido/)