diff --git a/gen_extclass.py b/gen_extclass.py
index 04c2c555..13b84fb4 100644
--- a/gen_extclass.py
+++ b/gen_extclass.py
@@ -23,10 +23,352 @@ def gen_extclass(args):
 //  This file automatically generated for %d-argument constructors by
 //  gen_extclass.py
 
-#ifndef EXTCLASS_PYGEN_DWA070900_H_
-# define EXTCLASS_PYGEN_DWA070900_H_
+#ifndef EXTENSION_CLASS_DWA052000_H_
+# define EXTENSION_CLASS_DWA052000_H_
 
+# include "pyconfig.h"
+# include "subclass.h"
+# include <vector>
+# include "none.h"
+# include "objects.h"
+# include "functions.h"
+# include <memory>
+# include "init_function.h"
+# include <typeinfo>
+# include <boost/smart_ptr.hpp>
+
+namespace py {
+
+// forward declarations
+class ExtensionInstance;
+template <class T> class InstanceHolder;
+template <class T, class U> class InstanceValueHolder;
+template <class Ptr, class T> class InstancePtrHolder;
+
+MetaClass<ExtensionInstance>* extension_meta_class();
+ExtensionInstance* get_extension_instance(PyObject* p);
+void report_missing_instance_data(ExtensionInstance*, Class<ExtensionInstance>*, const std::type_info&);
+void report_missing_ptr_data(ExtensionInstance*, Class<ExtensionInstance>*, const std::type_info&);
+void report_missing_class_object(const std::type_info&);
+void report_released_smart_pointer(const std::type_info&);
     
+template <class T, class U>
+struct ExtensionClassFromPython
+{
+};
+
+template <class T>
+T* check_non_null(T* p)
+{
+    if (p == 0)
+        report_released_smart_pointer(typeid(T));
+    return p;
+}
+
+template <class T> class HeldInstance;
+
+class ExtensionClassBase : public Class<ExtensionInstance>
+{
+ public:
+    ExtensionClassBase(const char* name);
+ protected:
+    void add_method(PyPtr<Function> method, const char* name);
+    void add_default_method(PyPtr<Function> method, const char* name);
+    void add_method(Function* method, const char* name);
+    void add_default_method(Function* method, const char* name);
+    
+    void add_constructor_object(Function*);
+    void add_setter_method(Function*, const char* name);
+    void add_getter_method(Function*, const char* name);
+};
+
+template <class T>
+class ClassRegistry
+{
+ public:
+    static Class<ExtensionInstance>* class_object()
+        { return static_class_object; }
+    static void register_class(py::Class<py::ExtensionInstance>*);
+    static void unregister_class(py::Class<py::ExtensionInstance>*);
+ private:
+    static py::Class<py::ExtensionInstance>* static_class_object;
+};
+
+#ifdef PY_NO_INLINE_FRIENDS_IN_NAMESPACE // back to global namespace for this GCC bug
+}
+#endif
+
+// This class' only job is to define from_python and to_python converters for T
+// and U. T is the class the user really intends to wrap. U is a class derived
+// from T with some virtual function overriding boilerplate, or if there are no
+// virtual functions, U = HeldInstance<T>.
+template <class T, class U = py::HeldInstance<T> >
+class PyExtensionClassConverters
+{
+ public:
+#ifdef BOOST_MSVC
+    // Convert return values of type T to python objects.  What happens if T is
+    // not copyable? Apparently there is no problem with g++ or MSVC unless this
+    // is actually used. With a conforming compiler we will have a problem.
+    friend PyObject* to_python(const T& x)
+        {
+            py::PyPtr<py::ExtensionInstance> result(create_instance(false));
+            result->add_implementation(
+                std::auto_ptr<py::InstanceHolderBase>(
+                    new py::InstanceValueHolder<T,U>(result.get(), x)));
+            return result.release();
+        }
+#else
+    friend py::Type<U> py_holder_type(const T&)
+        { return py::Type<U>(); }
+#endif
+    
+    PyExtensionClassConverters() {}
+    
+    // Convert to T*
+    friend T* from_python(PyObject* obj, py::Type<T*>)
+    {
+        // Downcast to an ExtensionInstance, then find the actual T
+        py::ExtensionInstance* self = py::get_extension_instance(obj);
+        typedef std::vector<py::InstanceHolderBase*>::const_iterator Iterator;
+        for (Iterator p = self->wrapped_objects().begin();
+             p != self->wrapped_objects().end(); ++p)
+        {
+            py::InstanceHolder<T>* held = dynamic_cast<py::InstanceHolder<T>*>(*p);
+            if (held != 0)
+                return held->target();
+        }
+        py::report_missing_instance_data(self, py::ClassRegistry<T>::class_object(), typeid(T));
+        throw py::ArgumentError();
+    }
+
+    // Convert to PtrType, where PtrType can be dereferenced to obtain a T.
+    template <class PtrType>
+    static PtrType& ptr_from_python(PyObject* obj, py::Type<PtrType>)
+    {
+        // Downcast to an ExtensionInstance, then find the actual T
+        py::ExtensionInstance* self = py::get_extension_instance(obj);
+        typedef std::vector<py::InstanceHolderBase*>::const_iterator Iterator;
+        for (Iterator p = self->wrapped_objects().begin();
+             p != self->wrapped_objects().end(); ++p)
+        {
+            py::InstancePtrHolder<PtrType, T>* held =
+                dynamic_cast<py::InstancePtrHolder<PtrType, T>*>(*p);
+            if (held != 0)
+                return held->ptr();
+        }
+        py::report_missing_ptr_data(self, py::ClassRegistry<T>::class_object(), typeid(T));
+        throw py::ArgumentError();
+    }
+
+    template <class PtrType>
+    static PyObject* ptr_to_python(PtrType x)
+        {
+            py::PyPtr<py::ExtensionInstance> result(create_instance(true));
+            result->add_implementation(
+                std::auto_ptr<py::InstanceHolderBase>(
+                    new py::InstancePtrHolder<PtrType,T>(x)));
+            return result.release();
+        }
+
+    static py::PyPtr<py::ExtensionInstance> create_instance(bool seek_base)
+        {
+            if (py::ClassRegistry<T>::class_object() == 0)
+                py::report_missing_class_object(typeid(T));
+            
+            py::Class<py::ExtensionInstance>* class_
+                = seek_base && py::ClassRegistry<T>::class_object()->bases().size() > 0
+                ? py::Downcast<py::Class<py::ExtensionInstance> >(
+                    py::ClassRegistry<T>::class_object()->bases()[0].get()).get()
+                : py::ClassRegistry<T>::class_object();
+            
+            return py::PyPtr<py::ExtensionInstance>(new py::ExtensionInstance(class_));
+        }
+
+
+    // Convert to const T*
+    friend const T* from_python(PyObject* p, py::Type<const T*>)
+        { return from_python(p, py::Type<T*>()); }
+
+    // Convert to T&
+    friend T& from_python(PyObject* p, py::Type<T&>)
+        { return *py::check_non_null(from_python(p, py::Type<T*>())); }
+
+    // Convert to const T&
+    friend const T& from_python(PyObject* p, py::Type<const T&>)
+        { return from_python(p, py::Type<T&>()); }
+
+    // Convert to T
+    friend const T& from_python(PyObject* p, py::Type<T>)
+        { return from_python(p, py::Type<T&>()); }
+
+    friend std::auto_ptr<T>& from_python(PyObject* p, py::Type<std::auto_ptr<T>&>)
+        { return ptr_from_python(p, py::Type<std::auto_ptr<T> >()); }
+    
+    friend std::auto_ptr<T>& from_python(PyObject* p, py::Type<std::auto_ptr<T> >)
+        { return ptr_from_python(p, py::Type<std::auto_ptr<T> >()); }
+    
+    friend const std::auto_ptr<T>& from_python(PyObject* p, py::Type<const std::auto_ptr<T>&>)
+        { return ptr_from_python(p, py::Type<std::auto_ptr<T> >()); }
+
+    friend PyObject* to_python(std::auto_ptr<T> x)
+        { return ptr_to_python(x); }
+
+    friend boost::shared_ptr<T>& from_python(PyObject* p, py::Type<boost::shared_ptr<T>&>)
+        { return ptr_from_python(p, py::Type<boost::shared_ptr<T> >()); }
+    
+    friend boost::shared_ptr<T>& from_python(PyObject* p, py::Type<boost::shared_ptr<T> >)
+        { return ptr_from_python(p, py::Type<boost::shared_ptr<T> >()); }
+    
+    friend const boost::shared_ptr<T>& from_python(PyObject* p, py::Type<const boost::shared_ptr<T>&>)
+        { return ptr_from_python(p, py::Type<boost::shared_ptr<T> >()); }
+
+    friend PyObject* to_python(boost::shared_ptr<T> x)
+        { return ptr_to_python(x); }
+};
+
+#ifndef BOOST_MSVC
+template <class T, class U>
+py::InstanceHolderBase*
+py_copy_to_new_value_holder(py::ExtensionInstance* p, const T& x, py::Type<U>)
+{
+    return new py::InstanceValueHolder<T,U>(p, x);
+}
+
+template <class T>
+PyObject* to_python(const T& x)
+{
+    py::PyPtr<py::ExtensionInstance> result(
+        PyExtensionClassConverters<T>::create_instance(false));
+    result->add_implementation(
+        std::auto_ptr<py::InstanceHolderBase>(
+            py_copy_to_new_value_holder(result.get(), x, py_holder_type(x))));
+    return result.release();
+}
+#endif
+
+#ifdef PY_NO_INLINE_FRIENDS_IN_NAMESPACE // back from global namespace for this GCC bug
+namespace py {
+using ::PyExtensionClassConverters;
+#endif
+
+template <class T> class InstanceHolder;
+
+class ReadOnlySetattrFunction : public Function
+{
+ public:
+    ReadOnlySetattrFunction(const char* name);
+    PyObject* do_call(PyObject* args, PyObject* keywords) const;
+    const char* description() const;
+ private:
+    String m_name;
+};
+
+// An easy way to make an extension base class which wraps T. Note that Python
+// subclasses of this class will simply be Class<ExtensionInstance> objects.
+//
+// U should be a class derived from T which overrides virtual functions with
+// boilerplate code to call back into Python. See extclass_demo.h for examples.
+// 
+// U is optional, but you won't be able to override any member functions in
+// Python which are called from C++ if you don't supply it. If you just want to
+// be able to use T in python without overriding member functions, you can omit
+// U.
+template <class T, class U = HeldInstance<T> >
+class ExtensionClass
+    : public PyExtensionClassConverters<T, U>, // This generates the to_python/from_python functions
+      public ExtensionClassBase
+{
+ public:
+    typedef T WrappedType;
+    typedef U CallbackType;
+    
+    // Construct with a name that comes from typeid(T).name(). The name only
+    // affects the objects of this class are represented through repr()
+    ExtensionClass();
+    
+    // Construct with the given name. The name only affects the objects of this
+    // class are represented through repr()
+    ExtensionClass(const char* name);
+    
+    ~ExtensionClass();
+
+    // define constructors
+""" % args
+        + gen_function(
+"""    template <%(class A%n%:, %)>
+    void def(Constructor<%(A%n%:, %)>)
+    // The following incantation builds a Signature1, Signature2,... object. It
+    // should _all_ get optimized away.
+    { add_constructor(
+        %(prepend(Type<A%n>::Id(),
+        %)        Signature0()%()%));
+    }
+""", args)
+        +
+"""
+    // define member functions. In fact this works for free functions, too -
+    // they act like static member functions, or if they start with the
+    // appropriate self argument (as a pointer), they can be used just like
+    // ordinary member functions -- just like Python!
+    template <class Fn>
+    void def(Fn fn, const char* name)
+    {
+        this->add_method(new_wrapped_function(fn), name);
+    }
+
+    // Define a virtual member function with a default implementation.
+    // default_fn should be a function which provides the default implementation.
+    // Be careful that default_fn does not in fact call fn virtually!
+    template <class Fn, class DefaultFn>
+    void def(Fn fn, const char* name, DefaultFn default_fn)
+    {
+        this->add_default_method(new_wrapped_function(default_fn), name);
+        this->add_method(new_wrapped_function(fn), name);
+    }
+
+    // Provide a function which implements x.<name>, reading from the given
+    // member (pm) of the T instance
+    template <class MemberType>
+    void def_getter(MemberType T::*pm, const char* name)
+    {
+        this->add_getter_method(new GetterFunction<T, MemberType>(pm), name);
+    }
+    
+    // Provide a function which implements assignment to x.<name>, writing to
+    // the given member (pm) of the T instance
+    template <class MemberType>
+    void def_setter(MemberType T::*pm, const char* name)
+    {
+        this->add_setter_method(new SetterFunction<T, MemberType>(pm), name);
+    }
+    
+    // Expose the given member (pm) of the T instance as a read-only attribute
+    template <class MemberType>
+    void def_readonly(MemberType T::*pm, const char* name)
+    {
+        this->add_setter_method(new ReadOnlySetattrFunction(name), name);
+        this->def_getter(pm, name);
+    }
+    
+    // Expose the given member (pm) of the T instance as a read/write attribute
+    template <class MemberType>
+    void def_read_write(MemberType T::*pm, const char* name)
+    {
+        this->def_getter(pm, name);
+        this->def_setter(pm, name);
+    }
+    
+ private:
+    typedef InstanceValueHolder<T,U> Holder;
+    
+    template <class Signature>
+    void add_constructor(Signature sig)
+    {
+        this->add_constructor_object(InitFunction<Holder>::create(sig));
+    }
+};
+
 // A simple wrapper over a T which allows us to use ExtensionClass<T> with a
 // single template parameter only. See ExtensionClass<T>, above.
 template <class T>
@@ -34,7 +376,7 @@ class HeldInstance : public T
 {
     // There are no member functions: we want to avoid inadvertently overriding
     // any virtual functions in T.
-public:""" % args
+public:"""
         + gen_functions(held_instance, args)
         + """
 protected:
@@ -66,8 +408,85 @@ public:
 private:
     Wrapper m_held;
 };
+""" +
+"""
+template <class PtrType, class HeldType>
+class InstancePtrHolder : public InstanceHolder<HeldType>
+{
+ public:
+    HeldType* target() { return &*m_ptr; }
+    PtrType& ptr() { return m_ptr; }
 
-#endif
+    InstancePtrHolder(PtrType ptr) : m_ptr(ptr) {}
+ private:
+    PtrType m_ptr;
+};
+
+class ExtensionInstance : public Instance
+{
+ public:
+    ExtensionInstance(PyTypeObject* class_);
+    ~ExtensionInstance();
+    
+    void add_implementation(std::auto_ptr<InstanceHolderBase> holder);
+
+    typedef std::vector<InstanceHolderBase*> WrappedObjects;
+    const WrappedObjects& wrapped_objects() const
+        { return m_wrapped_objects; }
+ private:
+    WrappedObjects m_wrapped_objects;
+};
+
+//
+// Template function implementations
+//
+
+template <class T, class U>
+ExtensionClass<T, U>::ExtensionClass()
+    : ExtensionClassBase(typeid(T).name())
+{
+    ClassRegistry<T>::register_class(this);
+}
+
+template <class T, class U>
+ExtensionClass<T, U>::ExtensionClass(const char* name)
+    : ExtensionClassBase(name)
+{
+    ClassRegistry<T>::register_class(this);
+}
+
+template <class T, class U>
+ExtensionClass<T, U>::~ExtensionClass()
+{
+    ClassRegistry<T>::unregister_class(this);
+}
+
+template <class T>
+inline void ClassRegistry<T>::register_class(Class<ExtensionInstance>* p)
+{
+    // You're not expected to create more than one of these!
+    assert(static_class_object == 0);
+    static_class_object = p;
+}
+
+template <class T>
+inline void ClassRegistry<T>::unregister_class(Class<ExtensionInstance>* p)
+{
+    // The user should be destroying the same object they created.
+    assert(static_class_object == p);
+    (void)p; // unused in shipping version
+    static_class_object = 0;
+}
+
+//
+// Static data member declaration.
+//
+template <class T>
+Class<py::ExtensionInstance>* ClassRegistry<T>::static_class_object;
+
+} // namespace py
+
+#endif // EXTENSION_CLASS_DWA052000_H_
 """)
 
 if __name__ == '__main__':