[Python-3000] [Python-3000-checkins] r62269 - in python/branches/py3k: Lib/test/test_getargs2.py Objects/abstract.c Python/getargs.c

[Trent Nelson]

> > Does this mean that floats can now be used as list indexes?
> > Preventing this was the motivation for introducing the nb_index slot.
>
> > from http://www.python.org/dev/peps/pep-0357 ::
> >
> >     The biggest example of why using nb_int would be a bad
> >     thing is that float objects already define the nb_int method, but
> >     float objects *should not* be used as indexes in a sequence.

> It sure did!  At least, between r62269 and r62279 ;-)  Ben pointed out
> my error, which I fixed in r62280.
>
>         Trent.

Hrrm.  I just re-read that PEP.  This stuck out:

    It is not possible to use the nb_int (and __int__ special method)
    for this purpose because that method is used to *coerce* objects
    to integers.  It would be inappropriate to allow every object that
    can be coerced to an integer to be used as an integer everywhere
    Python expects a true integer.  For example, if __int__ were used
    to convert an object to an integer in slicing, then float objects
    would be allowed in slicing and x[3.2:5.8] would not raise an error
    as it should.

I think I've pretty much violated the first few sentences with my change to PyNumber_Index().  Even with the change in r62280 which checks that we're not dealing with a float, it's still permitting anything else with an __int__ representation to pass through just fine.

Note that all of this originated from the following in test_args2:

class Long:
    def __int__(self):
        return 99

class Signed_TestCase(unittest.TestCase):
    ...
    def test_n(self):
        ...
        self.failUnlessEqual(99, getargs_n(Long()))

Before the change, %n was passing through to %l unless sizeof(long) != sizeof(size_t) (in convertsimple() -- Python/getargs.c).  Windows x64 is the only platform where this assertion holds true, which drew my attention to the problem.

The PEP's take on the situation would be that sequence[Long()] should fail (which isn't currently the case with my latest PyNumber_Index() changes).  If we want to adhere to the behaviour prescribed in the PEP, then it seems like PyNumber_Index() should be reverted back to its original state, and the handling of %n in convertsimple() should be be done without calling PyNumber_Index().

(I assume we *do* want to support `'%n' % Long()` though right, or should the test be done away with?)

Note that there's all sorts of problems with PyLong_AsSize_t() on Windows x64 when it comes to handling numbers close, equal or surpassing negative maximums.  (See first posting to issue 2440 for examples.)


        Trent.