python: hide cryptic shit in less cryptic wrappers.

UGH.

src/python/corrade/PyBuffer.h

@@ -29,6 +29,8 @@
 #include <Corrade/Containers/Pointer.h>
 #include <Corrade/Containers/StridedArrayView.h>
 
+#include "Corrade/Python.h"
+
 #include "bootstrap.h"
 
 namespace corrade {
@@ -45,17 +47,12 @@ template<class Class, bool(*getter)(Class&, Py_buffer&, int)> void enableBetterB
     CORRADE_INTERNAL_ASSERT(typeObject.as_buffer.bf_releasebuffer == pybind11::detail::pybind11_releasebuffer);
 
     typeObject.as_buffer.bf_getbuffer = [](PyObject *obj, Py_buffer *buffer, int flags) {
-        /* Stolen from pybind11::class_::def_buffer(). Not sure what exactly
-           it does, but I assume caster is implicitly convertible to Class& and
-           thus can magically access the actual Class from the PyObject. */
-        pybind11::detail::make_caster<Class> caster;
         CORRADE_INTERNAL_ASSERT(!PyErr_Occurred() && buffer);
-        CORRADE_INTERNAL_ASSERT(caster.load(obj, /*convert=*/false));
 
         /* Zero-initialize the output and ask the class to fill it. If that
            fails for some reason, give up */
         *buffer = Py_buffer{};
-        if(!getter(caster, *buffer, flags)) {
+        if(!getter(pyInstanceFromHandle<Class>(obj), *buffer, flags)) {
             CORRADE_INTERNAL_ASSERT(!buffer->obj);
             CORRADE_INTERNAL_ASSERT(PyErr_Occurred());
             return -1;

src/python/magnum/gl.cpp

@@ -39,6 +39,7 @@
 #include <Magnum/GL/RenderbufferFormat.h>
 #include <Magnum/Math/Color.h>
 
+#include "Corrade/Python.h"
 #include "Magnum/Python.h"
 
 #include "corrade/PyArrayView.h"
@@ -331,8 +332,7 @@ void gl(py::module& m) {
 
             /* Keep a reference to the renderbuffer to avoid it being deleted
                before the framebuffer */
-            /** @todo isn't there an API for this? */
-            self.attached.emplace_back(py::detail::get_object_handle(&renderbuffer, py::detail::get_type_info(typeid(GL::Renderbuffer))), true);
+            self.attached.emplace_back(pyObjectFromInstance(renderbuffer));
         }, "Attach renderbuffer to given buffer")
 
         .def_readonly("attached", &PyFramebuffer::attached, "Renderbuffer and texture objects referenced by the framebuffer");
@@ -390,8 +390,7 @@ void gl(py::module& m) {
 
             /* Keep a reference to the buffer to avoid it being deleted before
                the mesh */
-            /** @todo isn't there an API for this? */
-            self.buffers.emplace_back(py::detail::get_object_handle(&buffer, py::detail::get_type_info(typeid(GL::Buffer))), true);
+            self.buffers.emplace_back(pyObjectFromInstance(buffer));
         }, "Add vertex buffer", py::arg("buffer"), py::arg("offset"), py::arg("stride"), py::arg("attribute"))
         .def("draw", [](PyMesh& self, GL::AbstractShaderProgram& shader) {
             self.draw(shader);