[C++-sig] pass float from python to c++ as reference

[Sebastian Walter]

Hello,
I need to pass a float from Python to C++ as a reference. What is the best
way to do that? I can't find it in the unit tests:
boost_1_34_1/libs/python/test/test_builtin_converters.cpp


/* by_reference.cpp */
#include <boost/python.hpp>

void by_reference(double &x){
	x = 23.;
}
BOOST_PYTHON_MODULE(mymodule)
{
	using namespace boost::python;
	def("by_reference", by_reference);
}



/* by_reference.py */
import mymodule

x = 1.
print x
mymodule.by_reference(x)
print x

/* output */
>>Traceback (most recent call last):
>>  File "./test.py", line 7, in <module>
>>    mymodule.by_reference(x)
>>Boost.Python.ArgumentError: Python argument types in
>>    mymodule.by_reference(float)
>>did not match C++ signature:
>>    by_reference(double {lvalue})



thanks in advance,
Sebastian Walter