[Numpy-discussion] Anyone have a well-tested SWIG-based C++ STL valarray <=> numpy.array typemap to share?

[Xavier Gnata]

yeah! Looks good!
Thanks a lot.

Xavier
> Thanks!
>
> DG
>
> Lisandro Dalcin wrote:
>   
>> David, I'll try to show you what I do for a custom C++ class, of
>> course this does not solve the issue resizing (my class does not
>> actually support resizing, so this is fine for me):
>>
>> My custom class is a templatized one called DTable (is like a 2d
>> contiguous array), but currently I only instantiate it for 'int' and
>> 'double'. This class have two relevant methods: getShape(), returning
>> a std::pair, and getArray(), returning a reference to an underliing
>> std::vector. So I am able to automatically support array interface by
>> using this:
>>
>> First, I define a templatized utility function 'array_interface'
>>
>> %header %{
>> namespace numpy {
>>
>>   template<typename T> static char typechar() { return '\0'; }
>>   template<> static char typechar<int>()      { return  'i'; }
>>   template<> static char typechar<double>()   { return  'f'; }
>>
>>   template<typename T>
>>   static PyObject*
>>   array_interface(const DTable<T>* self)
>>   {
>>     const std::pair<int,int>& shape = self->getShape();
>>     const std::vector<T>&     data  = self->getArray();
>>     void* array = const_cast<T*>(&data[0]);
>>     char endian = PyArray_NATIVE;
>>     char kind   = typechar<T>();
>>     int  elsize = sizeof(T);
>>     return Py_BuildValue("{sNsNsNsN}",
>> 			 "shape",   Py_BuildValue("ii", shape.first, shape.second),
>> 			 "typestr", PyString_FromFormat("%c%c%d", endian, kind, elsize),
>> 			 "data",    Py_BuildValue("NO", PyLong_FromVoidPtr(array), Py_False),
>> 			 "version", PyInt_FromLong(3));
>>   }
>> }
>> %}
>>
>> Now define a SWIG macro to apply it to instantiations of my class
>>
>> %define %array_interface(Class)
>> %extend Class { PyObject* __array_interface__; }
>> %{
>> #define %mangle(Class) ##_## __array_interface__ ## _get(_t) \
>>         numpy::array_interface(_t)
>> #define %mangle(Class) ##_## __array_interface__ ## _set(_t, _val) \
>>         SWIG_exception_fail(SWIG_AttributeError, "read-only attribute")
>> %}
>> %enddef
>>
>> and finally instantiate my class with different names for 'int' and
>> 'double' in SWIG and finally apply previous macro
>>
>>
>> %template(DTableI) DTable<int>;
>> %template(DTableS) DTable<double>;
>>
>> %array_interface( DTable<int> );
>> %array_interface( DTable<double> );
>>
>> I think you can implement someting similar for std::vector,
>> std::valarray, or whatever... For use other data types, the only you
>> need is to specialize the 'typecode' function.
>>
>> Hope this help you.
>>
>>
>> On 9/4/07, David Goldsmith <David.L.Goldsmith at noaa.gov> wrote:
>>   
>>     
>>> Anyone have a well-tested SWIG-based C++ STL valarray <=> numpy.array
>>> typemap to share?  Thanks!
>>>
>>> DG
>>> --
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>>> Numpy-discussion mailing list
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>>>     
>>>       
>>   
>>     
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>   


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Xavier Gnata
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