[Numpy-discussion] Code generator bug and fix?

[Travis E. Oliphant]

Charles R Harris wrote:
>
>
> On Mon, Apr 21, 2008 at 8:53 PM, Charles R Harris 
> <charlesr.harris@gmail.com <mailto:charlesr.harris@gmail.com>> wrote:
>
>
>
>     On Mon, Apr 21, 2008 at 8:28 PM, Travis E. Oliphant
>     <oliphant@enthought.com <mailto:oliphant@enthought.com>> wrote:
>
>         Charles R Harris wrote:
>         > I've gotten my own python class with a logical_not method to
>         work
>         > correctly if I goto
>         numpy/core/code_generators/generate_umath.py and
>         > change
>         I need more context for this.   Why does the umath generator
>         matter for
>         your python class?
>         >
>         > 'logical_not' :
>         >     Ufunc(1, 1, None,
>         >           'returns not x elementwise.',
>         >           TD(noobj, out='?'),
>         >           TD(M, f='logical_not', out='?'),
>         >           ),
>         >
>         > to
>         >
>         > 'logical_not' :
>         >     Ufunc(1, 1, None,
>         >           'returns not x elementwise.',
>         >           TD(noobj, out='?'),
>         >           TD(M, f='logical_not'),
>         >           ),
>         >
>         Why is this an error?   Is the difference only removing the out
>         variable?  It's been a while since I reviewed this code, so
>         what does
>         removing the out variable do functionally (What is the
>         difference in the
>         ufunc that is generated)?
>
>
>     The way it is, it passes a boolean array to the PyUFunc_O_O_method
>     loop where the loop is expecting an object array. I checked the
>     step size to see this, and that's also how the generated signature
>     reads. Consequently, when the reference count is decremented bad
>     things happen. I suspect this hasn't been seen before because it
>     hadn't been tried. I wrote loop tests before cleaning up the loop
>     code and the bug turned up then.
>
>     My guess is that here M means object called through non-Python
>     method (logical_not), and omitting out means the output type is
>     the same as the input. I suspect that '?' should do the same thing
>     and that there might be a bug in the function dispatcher or the
>     signature generator, but I'm not clear on that yet.
>
>
> If out is omitted, the output types matches the input types. Here's 
> where the output types are generated:
>
>     def finish_signature(self, nin, nout):
>         if self.in_ is None:
>             self.in_ = self.type * nin
>         assert len(self.in_) == nin
>         if self.out is None:
>             self.out = self.type * nout
>         assert len(self.out) == nout
>
> So that seems like the right thing to do. I still don't know what  '?' 
> means, though.

Thanks Chuck,

I get it now (I should have spent a minute looking at the code).  The 
'?' is the character code for "boolean"

So, I think you are right about the bug.

-Travis