mhearne808 wrote: > I have a question about how dynamically loaded C++ modules work, which > I will phrase as a hypothetical scenario involving the Numeric module. > Please understand that I don't really care about Numeric per se, it's > just a useful example of a module that defines a generally useful data > type. > > Let's say I want to create a C++ Python extension module that has > methods accepting the Numeric array type as input, and also create > these arrays as output. > > In order to make this work, do I have to statically link against the > Numeric source, or do I only have to include the headers, under the > assumption (??) that the Numeric functionality will be available > because the Python executable has dynamically loaded it?
Here's how Numeric/numarray/numpy do it (I'll discuss numpy since it is the currently developed one): Pointers to each of the API items that we want to export, types and functions mostly, are packed into a void** array, PyArray_API. A common header file is used by the numpy extension module that provides the API (multiarraymodule.so) and each of the modules that use the API. We use #ifdefs to determine whether to use real prototypes (for multiarray) or #defines that index into PyArray_API and cast the function pointer there to the appopriate prototype (for everybody else). In initmultiarray(), we actually pack PyArray_API with the appropriate pointers and create a PyCObject that points to the beginning of the array. The CObject is assigned to multiarray._ARRAY_API . We define a function import_array() for the API-users that will import multiarray, get the object _ARRAY_API and assign pointer to the beginning of the array to void **PyArray_API. import_array() is supposed to be called in the initialization function of the other extension modules. That will make sure that multiarray is imported and the function pointers are available for dereferencing. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
