[Numpy-discussion] [C++-sig] Overloading sqrt(5.5)*myvector

Bruce Sherwood Bruce_Sherwood@ncsu....
Fri Dec 28 23:47:09 CST 2007


I realized belatedly that I should upgrade from Boost 1.33 to 1.34. 
Alas, that didn't cure my problem.

Bruce Sherwood

Bruce Sherwood wrote:
> I should have added: This structure worked with the older version of 
> VPython which used Numeric, but it doesn't work in the beta version 
> which uses numpy. Since I don't know enough about either numpy or Boost, 
> I'm left guessing which subsystem is the source of my difficulties, and 
> clueless about how to remedy them.
>
> Bruce Sherwood
>
> Bruce Sherwood wrote:
>   
>> Thanks for the comment, which limits the range of possible solutions. 
>> The VPython vector class is implemented in C++, not in Python. I made up 
>> the simple test in my previous note to try out the solution that had 
>> been offered and which you have usefully ruled out. Here is the relevant 
>> part of the vector class, which indeed doesn't look like an ndarray:
>>
>> inline vector
>> operator*( const double s) const throw()
>> { return vector( s*x, s*y, s*z); }
>>
>> and here is the free function for right multiplication:
>>
>> inline vector
>> operator*( const double& s, const vector& v)
>> { return vector( s*v.x, s*v.y, s*v.z); }
>>
>> Maybe the unsolvable problem is in the Boost definitions:
>>
>> py::class_<vector>("vector", py::init< py::optional<double, double, 
>> double> >())
>>      .def( self * double())
>>      .def( double() * self)
>>
>> Left multiplication is fine, but right multiplication isn't.
>>
>> Bruce Sherwood
>>
>> Robert Kern wrote:
>>   
>>     
>>> Bruce Sherwood wrote:
>>>   
>>>     
>>>       
>>>> Thanks for the suggestion. It hadn't occurred to me to try to override 
>>>> numpy as you suggest. However, when I try the code shown below as the 
>>>> start of a test of this scheme, I get the following error:
>>>>
>>>> Traceback (most recent call last):
>>>>   File "C:\Documents and Settings\Bruce\My 
>>>> Documents\0VPythonWork\vectors.py", line 24, in <module>
>>>>     numpy.float64.__mul__ = new_mul
>>>> TypeError: can't set attributes of built-in/extension type 'numpy.float64'
>>>>
>>>> I'm copying this to the numpy discussion list, as maybe someone there 
>>>> will see where to go starting from your suggestion.
>>>>     
>>>>       
>>>>         
>>> Like most (or all) builtin-types, the numpy float scalars do not permit
>>> replacing their methods from Python.
>>>
>>> I'm not familiar with vpython's vector. If you can make it "not look like an
>>> ndarray", then you should be able to just implement __rmul__ on vector.
>>>
>>>   
>>>     
>>>       
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>>     
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