[PyQt] SIP Pointer Confusion

[Phil Thompson]

On 30 Sep 2016, at 1:43 am, Jay L. <jlaura at asu.edu> wrote:
> 
> Just starting to dig into SIP. I have a .h file that contains the following public method:
> 
> void Allocate(int width, int height, int pitch, bool withHost, float *devMem = NULL, float* hostMem = NULL); 
> 
>  have created a corresponding .sip file:
> 
> 1 //SIP wrapper for CUDA Image 
> 2 
> 3 class CudaImage 
> 4 { 
> 5 %TypeHeaderCode 
> 6 #include "cudaImage.h" 
> 7 %End 
> 8 
> 9 public: 
> 10 CudaImage(); 
> 11 
> 12 void Allocate(int width, int height, int pitch, bool withHost, float *devMem=NULL, float *hostMem=NULL) /KeywordArgs="All"/; 
> 13 double Download(); 
> 14 
> 15 
> 16 int width; 
> 17 int height; 
> 18 int pitch; 
> 19 };
> 
> Using CMake, I have the build working, can import the module into Python and can call the constructor (so limited success). I can also call the Allocate method. Unfortunately, on the Python side, I can not get the float *devMem=NULL or float *hostMem=Nullarguments exposed. I have been over the SIP documentation and no Annotations are leaping out as missing.
> 
> The ultimate goal is to pass a numpy array (.data attribute I believe) to the hostMemargument.
> 
> How does one go about exposing pointers in SIP? What about pointers with a default, NULL, argument?

Pointers to fundamental types are (by default) treated as a way to return a value from the method and not pass a value to it - see the /In/ annotation.

You should then hit the problem that you will have to provide hand-written code to handle those arguments because SIP doesn't know how to convert them to a Python object. You probably need to declare the types as SIP_PYOBJECT and handle the conversion in %MethodCode. Alternatively if that is a common situation in your API then consider defined a mapped type.

If numpy arrays support the buffer protocol then you should look at exploiting that. You should also look at sip.array and sipConvertToArray().

Phil