[Python-Dev] Unicode exception indexing

["Martin v. Löwis"]

> I started such hack for the UTF-8 codec... It is really tricky, we should not 
> do that!

With the proper encapsulation, it's not that tricky. I have written
functions PyUnicode_IndexToWCharIndex and PyUnicode_WCharIndexToIndex,
and PyUnicodeEncodeError_GetStart and friends would use that function.
I'd also need new functions PyUnicodeEncodeError_GetStartIndex to access
the "true" start field.

>> That would be expensive to compute
> 
> Yeah, O(n) should be avoided when is it possible.

Ok. I'll wait half a day or so for people to reconsider (now knowing
that it's actually feasible to be fully backwards compatible); if nobody
speaks up, I go ahead and accept the breakage.

Regards,
Martin