Near the top of your extension module add the line:
#include "numarray.h"
In your extension module's initialization function, add the line:
import_libnumarray();
import_libnumarray() is actually a macro which sets up a pointer to the numarray C-API jump table. If you forget to call import_libnumarray(), your extension module will crash as soon as you call a numarray API function, because your application will attempt to dereference a NULL pointer.
Note that there is also a Numeric compatible API which substitutes arrayobject.h for numarray.h and import_array() for import_libnumarray() respectively.
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