[Python-Dev] PEP for adding an sq_index slot so that any object, a or b, can be used in X[a:b] notation

[Travis E. Oliphant]

Adam Olsen wrote:
> On 2/9/06, Travis Oliphant <oliphant.travis at ieee.org> wrote:
> 
>>Guido seemed accepting to this idea about 9 months ago when I spoke to
>>him.  I finally got around to writing up the PEP.   I'd really like to
>>get this into Python 2.5 if possible.
> 
> 
> -1
> 
> I've detailed my reasons here:
> http://mail.python.org/pipermail/python-dev/2006-January/059851.html
> 
> In short, there are purely math usages that want to convert to int
> while raising exceptions from inexact results.  The name __index__
> seems inappropriate for this, and I feel it would be cleaner to fix
> float.__int__ to raise exceptions from inexact results (after a
> suitable warning period and with a trunc() function added to math.)
>

I'm a little confused.  Is your opposition solely due to the fact that 
you think float's __int__ method ought to raise exceptions and the 
apply_slice code should therefore use the __int__ slot?

In theory I can understand this reasoning.  In practice, however, the 
__int__ slot has been used for "coercion" and changing the semantics of 
int(3.2) at this stage seems like a recipe for lots of code breakage.  I 
don't think something like that is possible until Python 3k.

If that is not your opposition, please be more clear. Regardless of how 
it is done, it seems rather unPythonic to only allow 2 special types to 
be used in apply_slice and assign_slice.

-Travis