don't throw an exception when python deallocates an object which still exists on the C++ side

include/pybind/cast.h

@@ -292,6 +292,9 @@ public:
     PYBIND_TYPE_CASTER(void_type, "None");
 };
 
+template <> class type_caster<void> : public type_caster<void_type> {
+};
+
 template <> class type_caster<bool> {
 public:
     bool load(PyObject *src, bool) {

include/pybind/pybind.h

@@ -883,6 +883,8 @@ public:
 
 inline function get_overload(const void *this_ptr, const char *name)  {
     handle py_object = detail::get_object_handle(this_ptr);
+    if (!py_object)
+        return function();
     handle type = py_object.get_type();
     auto key = std::make_pair(type.ptr(), name);
 

include/pybind/pytypes.h

@@ -400,7 +400,7 @@ inline handle get_object_handle(const void *ptr) {
     auto instances = get_internals().registered_instances;
     auto it = instances.find(ptr);
     if (it == instances.end())
-        throw std::runtime_error("Internal error: could not acquire Python handle of a C++ object");
+        return handle();
     return it->second;
 }