[C++-sig] How do I detect a Python subclass (with 3rd party pointer) ?

[English, Mark]

If I expose a class through Boost Python, is there a way to discover that the parameter to a wrapped function
is an instance of a sub-class defined in Python, rather than an instance of the actual exposed class ?
Some kind of lookup in the converter::registry ?
Some kind of attribute added to exposed classes by a visitor ?
Something else ?

For example:
// Start cpp
#include <smart_ptr.h>
class ExampleBase{};
class Example1 : public ExampleBase {};
class Example2 : public ExampleBase {};
//...
class ExampleN : public ExampleBase {};

void testFunction(boost::python::object objTest)
{
  // Some kind of check for exposed classes here
}

BOOST_PYTHON_MODULE(test)
{
  class_<Example, smart_ptr<Example> >("Example");
  class_<Example1, bases<Example>, smart_ptr<Example1> >("Example1");
  class_<Example2, bases<Example>, smart_ptr<Example2> >("Example2");
  //...
  class_<ExampleN, bases<Example>, smart_ptr<ExampleN> >("ExampleN");

  def("testFunction", &testFunction);
}

// End of cpp
#Start of py
import test
class PyDerived(test.Example2): pass
class External(object): pass
ex2 = test.Example2()
pyd = PyDerived()
ext = External()
test.testFunction(ex2) #Handled by straight C++ conversion
test.testFunction(pyd) #<- Want C++ code to realise this is a Python derived class
test.testFunction(ext) #<- Want C++ code to realise this is a Python class unrelated to C++ code
#End of py
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