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

[Guido van Rossum]

> That's fine.  But what i'm trying to say is there's a migration issue:
> this decision is a significant change from current behaviour, and it
> worries me that we would let this change pass silently without any
> grace period.

And others have said the exact same thing already.

But there is no backwards compatibility issue.  Correct programs
currently never ask for '' in 'abc' because that's guaranteed to raise
a TypeError.  Backwards compatibility guarantees have always had to
use the qualification "except for programs that rely on XYZ raising an
exception" so you can't argue that reasonable code could expect the
TypeError either.

The only issue is whether certain programming mistakes come to light a
little later now that '' in 'abc' no longer raises TypeError.  I'm
willing to accept that in order to make teaching the feature easier:
s1 in s2 means the same thing as s2.find(s1)>=0.

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