[Numpy-discussion] Why am I getting a FutureWarning with this code?

[Steve Spicklemire]

Ah, thanks. I'll have to break out gdb for that!

thanks,
-steve

> On Dec 22, 2014, at 11:28 AM, Robert Kern <robert.kern at gmail.com> wrote:
> 
> On Mon, Dec 22, 2014 at 10:35 AM, Steve Spicklemire <steve at spvi.com> wrote:
> >
> > I’m working on visual python (http://vpython.org) which lists numpy among its dependencies.
> >
> > I recently updated my numpy installation to 1.9.1 and I’m now encountering this error:
> >
> > /usr/local/Cellar/python/2.7.8_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/VPython-6.10-py2.7-macosx-10.10-x86_64.egg/visual_common/materials.py:70: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
> >   self.__setattr__(key, value)
> >
> > Oddly, the code in question looks like this:
> >
> >
> >      62 from . import cvisual
> >      63 from numpy import array, reshape, fromstring, ubyte, ndarray, zeros, asarray
> >      64 import os.path, math
> >      65
> >      66 class raw_texture(cvisual.texture):
> >      67     def __init__(self, **kwargs):
> >      68         cvisual.texture.__init__(self)
> >      69         for key, value in kwargs.items():
> >      70             self.__setattr__(key, value)
> 
> The answer is in the implementation of cvisual.texture somewhere. This is Boost.Python C++ code, so there's a fair bit of magic going on such that I can't pinpoint the precise line that's causing this, but I suspect that it might be this one:
> 
> https://github.com/BruceSherwood/vpython-wx/blob/master/src/python/numeric_texture.cpp#L258
> 
> When `data` is assigned, this line checks if the value is None so that it can raise an error to tell you not to do that (I believe, from the context, that `py::object()` is the Boost.Python idiom for getting the None singleton). I *think*, but am not positive, that Boost.Python converts the C++ == operator into a Python == operation, so that would trigger this FutureWarning.
> 
> So VPython is the code that needs to be fixed to do an identity comparison with None rather than an equality comparison.
> 
> --
> Robert Kern
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