> > 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.
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