Travis Oliphant wrote: > The problem here is that from Python NumPy has no way to create an > ndarray from a pointer. Doing this creates a situtation where it is > unclear who owns the memory. It is probably best to wrap the pointer > into some kind of object exposing the buffer protocol and then pass > that to frombuffer (or ndarray.__new__). Yep thats where I just ended up:
from ctypes import * import numpy as N ... func = pythonapi.PyBuffer_FromMemory func.restype = py_object buffer = func( im.imageData, size_of_the_data ) <----imageData = ctypes.LP_c_ubyte object return N.frombuffer( buffer, N.uint8 ) Works! Im curious though: the several projects recently using ctypes and numpy to wrap libraries (Pygame SDL, OpenGL, svm) must have come across the issue of using a creating a numpy array from a ctypes pointer. Ill have to look further. > When an ndarray is using memory that is not its own, it expects > another object to be "in charge" of that memory and the ndarray will > point its base attribute to it and increment its reference count. > What should the object that is "in charge" of the memory be? > Perhaps a suitable utility function could be created that can work > with ctypes to create ndarrays from ctypes memory locations and either > own or disown the data. > I suppose that is still the case w/ PyBuffer_From.. above. That is, the underlying im.imageData pointer can not be released before buffer. Mark > This needs to be thought through a bit, however. > > -Travis > > > >> The attributes in nparray.__array_interface_ are not writable, so no >> joy there. >> >> On the C side the PyArray_SimpleNewFromData( ..dimensions, ...data >> ptr) C API does the job nicely. Is there a ctypes paradigm for >> SimpleNew...? >> >> Mark >> >> >> >> ------------------------------------------------------------------------- >> >> Using Tomcat but need to do more? Need to support web services, >> security? >> Get stuff done quickly with pre-integrated technology to make your >> job easier >> Download IBM WebSphere Application Server v.1.0.1 based on Apache >> Geronimo >> http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 >> _______________________________________________ >> Numpy-discussion mailing list >> Numpy-discussion@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/numpy-discussion >> > ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Numpy-discussion mailing list Numpy-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/numpy-discussion
