[Numpy-discussion] strange multiplication behavior with numpy.float64 and ndarray subclass

Darren Dale dsdale24@gmail....
Sun Mar 8 18:14:33 CDT 2009


On Sun, Mar 8, 2009 at 7:00 PM, Charles R Harris
<charlesr.harris@gmail.com>wrote:

>
>
> On Sun, Mar 8, 2009 at 4:42 PM, Darren Dale <dsdale24@gmail.com> wrote:
>
>> On Sun, Mar 8, 2009 at 12:31 PM, Darren Dale <dsdale24@gmail.com> wrote:
>>
>>> On Wed, Jan 21, 2009 at 12:43 PM, Pierre GM <pgmdevlist@gmail.com>wrote:
>>>
>>>>
>>>> On Jan 21, 2009, at 11:34 AM, Darren Dale wrote:
>>>>
>>>> > I have a simple test script here that multiplies an ndarray subclass
>>>> > with another number. Can anyone help me understand why each of these
>>>> > combinations returns a new instance of MyArray:
>>>> >
>>>> > mine = MyArray()
>>>> > print type(np.float32(1)*mine)
>>>> > print type(mine*np.float32(1))
>>>> > print type(mine*np.float64(1))
>>>> > print type(1*mine)
>>>> > print type(mine*1)
>>>> >
>>>> > but this one returns a np.float64 instance?
>>>>
>>>> FYI, that's the same behavior as observed in ticket #826. A first
>>>> thread addressed that issue
>>>> http://www.mail-archive.com/numpy-discussion@scipy.org/msg13235.html
>>>> But so far, no answer has been suggested.
>>>> Any help welcome.
>>>
>>>
>>> I believe ticket #826 can be solved with the application of this patch:
>>>
>>>
>>> $ svn diff scalarmathmodule.c.src
>>> Index: scalarmathmodule.c.src
>>> ===================================================================
>>> --- scalarmathmodule.c.src      (revision 6566)
>>> +++ scalarmathmodule.c.src      (working copy)
>>> @@ -566,6 +566,10 @@
>>>          Py_DECREF(descr1);
>>>          return ret;
>>>      }
>>> +    else if (PyArray_GetPriority(a, PyArray_SUBTYPE_PRIORITY) > \
>>> +            PyArray_SUBTYPE_PRIORITY) {
>>> +        return -2;
>>> +    }
>>>      else if ((temp = PyArray_ScalarFromObject(a)) != NULL) {
>>>          int retval;
>>>          retval = _@name@_convert_to_ctype(temp, arg1);
>>>
>>>
>>> I've run the unit tests and get the same results with and without the
>>> patch applied, but it solves the problem in my script and also the problem
>>> with masked arrays.
>>
>>
>> Here is a test for this patch, maybe issue #826 can be closed.
>>
>> Index: numpy/core/tests/test_umath.py
>> ===================================================================
>> --- numpy/core/tests/test_umath.py      (revision 6575)
>> +++ numpy/core/tests/test_umath.py      (working copy)
>> @@ -253,6 +253,17 @@
>>          self.failUnless(isinstance(x, with_wrap))
>>          assert_array_equal(x, np.array((1, 2, 3)))
>>
>> +    def test_priority_with_scalar(self):
>> +        # test fix for bug #826:
>> +        class A(np.ndarray):
>> +            __array_priority__ = 10
>> +            def __new__(cls):
>> +                return np.asarray(1.0, 'float64').view(cls).copy()
>> +        a = A()
>> +        x = np.float64(1)*a
>> +        self.failUnless(isinstance(x, A))
>> +        assert_array_equal(x, np.array(1))
>> +
>>      def test_old_wrap(self):
>>          class with_wrap(object):
>>              def __array__(self):
>>
>> __
>
>
> Added in r6578... Chuck
>

Thank you very much.
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