[NumPy-Tickets] [NumPy] #1594: numpy.dtype('float64') == None returns True

[NumPy Trac]

#1594: numpy.dtype('float64') == None returns True
-------------------------------+--------------------------------------------
 Reporter:  Zbyszek_Szmek      |       Owner:  somebody   
     Type:  defect             |      Status:  new        
 Priority:  normal             |   Milestone:  Unscheduled
Component:  Other              |     Version:  devel      
 Keywords:  dtype, comparison  |  
-------------------------------+--------------------------------------------
Changes (by Zbyszek_Szmek):

  * milestone:  2.0.0 => Unscheduled


Comment:

 From numpy-discussion...

 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.

-- 
Ticket URL: <http://projects.scipy.org/numpy/ticket/1594#comment:1>
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