[Numpy-discussion] bug in dtype.__eq__ method ?

[Zbyszek Szmek]

On Wed, Aug 25, 2010 at 12:41:37PM -0500, Travis Oliphant wrote:
> 
> On Aug 23, 2010, at 11:55 AM, Zbyszek Szmek wrote:
> 
> > On Mon, Aug 23, 2010 at 06:50:09PM +0200, Tiziano Zito wrote:
> >> hi all, 
> >> we just noticed the following weird thing:
> >> 
> >> $ python
> >> Python 2.6.6rc2 (r266rc2:84114, Aug 18 2010, 07:33:44) 
> >> [GCC 4.4.5 20100816 (prerelease)] on linux2
> >> Type "help", "copyright", "credits" or "license" for more information.
> >>>>> import numpy
> >>>>> numpy.version.version
> >> '2.0.0.dev8469'
> > Also with numpy.version.version == 1.3.0.
> 
> This certainly looks odd.   If you can file a bug-report that would be great. 

arraydescr_richcompare calls PyArray_DescrConverter, which converts None
to PyArray_DEFAULT...

/*NUMPY_API
 * Get typenum from an object -- None goes to PyArray_DEFAULT
 * This function takes a Python object representing a type and converts it
 * to a the correct PyArray_Descr * structure to describe the type.
 *
 * Many objects can be used to represent a data-type which in NumPy is
 * quite a flexible concept.
 *
 * This is the central code that converts Python objects to
 * Type-descriptor objects that are used throughout numpy.
 * new reference in *at
 */
NPY_NO_EXPORT int
PyArray_DescrConverter(PyObject *obj, PyArray_Descr **at)

So:
>>> numpy.dtype('float32') == '<f4'
True
>>> numpy.dtype('float32') == 'float64'
False
>>> numpy.dtype('float32') == 'float32'
True
>>> numpy.dtype('float32') == 'float33'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: data type not understood

I think that this automatic conversion is pretty dangerous, especially in case
of None.

Best,
Zbyszek