I'm embedding Python (using boost::python) into an application plugin
that uses callbacks. Essentially, I want to do something like:
In Python (say test.py):
def do_something():
...
register_callback(do_something)
And on the C++ side I register the register_callback() function:
void register_callback(boost::python::object& o)
{
// Access some persistent state information
}
BOOST_PYTHON_MODULE(foo)
{
boost::python::def("register_callback", register_callback);
}
void library_entry()
{
PyImport_AppendInittab("foo", initfoo);
PyInitialize();
// Create some persistent state information
boost::python::exec_file("test.py", ...);
}
The issue here is that I need to create the Python context and store
things away in an opaque pointer I return to the application. And when
Python calls back into the C++, I need to recover that opaque value.
For example:
Application -- (calls) --> my C++ library -- (runs) --> Python script
-- (calls) --> my C++ library
For that last step, I need to recover some opaque data. Further, I
need that opaque data to be persistent. The calls into my C++ library
are callbacks from the application. The issue I'm having is trying to
figure out how to pass that state information to the C++
register_callback() function. I've tried something like:
namespace bp = boost::python;
class state_info_t
{
};
void register_callback(std::shared_ptr<state_info_t>& state, bp::object& o);
{
// Access some persistent state information
}
// Create some persistent state information
std::shared_ptr<state_info_t> state = std::make_shared<state_info_t>();
PyImport_AppendInittab("foo", initfoo);
Py_Initialize();
std::shared_ptr<bp::object> main_module =
std::make_shared<bp::object>(bp::handle<>(bp::borrowed(PyImport_AddModule("__main__"))));
bp::object main_namespace = main_module->attr("__dict__");
std::shared_ptr<bp::object> foo_module =
std::make_shared<bp::object>(bp::handle<>(PyImport_ImportModule("foo")));
main_namespace["foo"] = *foo_module;
bp::scope foo_scope(*foo_module);
// Both of these fail with _a lot_ of errors, most related to "no
matching function call to 'get_signature'
bp::def("register_callback",
[&](bp::object& o) { register_callback(state, o); },
bp::arg("func"));
bp::def("register_callback",
std::bind(register_callback, state, std::placeholders::_1),
bp::arg("func"));
The other thought I had was to store the persistent data in the
module's dictionary. But I don't know how to recover it in the
callback. For example:
// Create some persistent state information
std::shared_ptr<state_info_t> state = std::make_shared<state_info_t>();
PyImport_AppendInittab("foo", initfoo);
Py_Initialize();
std::shared_ptr<bp::object> main_module =
std::make_shared<bp::object>(bp::handle<>(bp::borrowed(PyImport_AddModule("__main__"))));
bp::object main_namespace = main_module->attr("__dict__");
std::shared_ptr<bp::object> foo_module =
std::make_shared<bp::object>(bp::handle<>(PyImport_ImportModule("foo")));
bp::object foo_namespace = main_module->attr("__dict__");
main_namespace["foo"] = *foo_module;
foo_namespace["state"] = bp::handle<>(state); // Whatever the
appropriate wrapper is
Then in C++ side of register_callback:
void register_callback(bp::object& o)
{
// How do I extract "state" from the context?
}
I'm not keen on this last one, since it exposes the state information
to the script.
I don't want to make the state information global since there may be
multiple running Python instances. And regardless, with multiple
Python instances I still need a way to determine which Python instance
is running to select the appropriate state information.
Any suggestions?
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