Improve TypeError exceptions

- use pybind11 API instead of Python C API
- provide more informative error messages

core/python/bindings/src/core.cpp

@@ -86,9 +86,8 @@ void setForwardedProperties(Stage& self, const py::object& names) {
 			for (auto item : names)
 				s.emplace(item.cast<std::string>());
 	} catch (const py::cast_error& e) {
-		// manually translate cast_error to type error
-		PyErr_SetString(PyExc_TypeError, e.what());
-		throw py::error_already_set();
+		// translate cast_error to type_error with an informative message
+		throw py::type_error("Expecting a string or a list of strings");
 	}
 	self.setForwardedProperties(s);
 }

core/python/bindings/src/properties.cpp

@@ -43,6 +43,14 @@ namespace moveit {
 namespace python {
 namespace {
 
+/** In order to assign new property values in Python, we need to convert the Python object
+ *  to a boost::any instance of the correct type. As the C++ type cannot be inferred from
+ *  the Python type, we can support this assignment only for a few basic types (see fromPython())
+ *  as well as ROS message types. For other types, a generic assignment via
+ *  stage.properties["property"] = value
+ *  is not possible. Instead, use the .property<Type> declaration on the stage to allow for
+ *  direct assignment like this: stage.property = value
+ **/
 class PropertyConverterRegistry
 {
 	struct Entry
@@ -102,10 +110,8 @@ py::object PropertyConverterRegistry::toPython(const boost::any& value) {
 
 	auto it = REGISTRY_SINGLETON.types_.find(value.type());
 	if (it == REGISTRY_SINGLETON.types_.end()) {
-		std::string msg("No Python -> C++ conversion for: ");
-		msg += boost::core::demangle(value.type().name());
-		PyErr_SetString(PyExc_TypeError, msg.c_str());
-		throw py::error_already_set();
+		std::string name = boost::core::demangle(value.type().name());
+		throw py::type_error("No Python -> C++ conversion for: " + name);
 	}
 
 	return it->second.to_(value);
@@ -115,12 +121,9 @@ std::string rosMsgName(PyObject* object) {
 	py::object o = py::reinterpret_borrow<py::object>(object);
 	try {
 		return o.attr("_type").cast<std::string>();
-	} catch (const py::error_already_set&) {
-		// change error to TypeError
-		std::string msg = o.attr("__class__").attr("__name__").cast<std::string>();
-		msg += " is not a ROS message type";
-		PyErr_SetString(PyExc_TypeError, msg.c_str());
-		throw py::error_already_set();
+	} catch (const py::error_already_set& e) {
+		// object is not a ROS message type, return it's class name instead
+		return o.attr("__class__").attr("__name__").cast<std::string>();
 	}
 }
 
@@ -138,12 +141,8 @@ boost::any PropertyConverterRegistry::fromPython(const py::object& po) {
 
 	const std::string& ros_msg_name = rosMsgName(o);
 	auto it = REGISTRY_SINGLETON.msg_names_.find(ros_msg_name);
-	if (it == REGISTRY_SINGLETON.msg_names_.end()) {
-		std::string msg("No Python -> C++ conversion for: ");
-		msg += ros_msg_name;
-		PyErr_SetString(PyExc_TypeError, msg.c_str());
-		throw py::error_already_set();
-	}
+	if (it == REGISTRY_SINGLETON.msg_names_.end())
+		throw py::type_error("No C++ conversion available for (property) type: " + ros_msg_name);
 
 	return it->second->second.from_(po);
 }

core/python/bindings/src/stages.cpp

@@ -323,6 +323,8 @@ void export_stages(pybind11::module& m) {
 
 			For an example, see :ref:`How-To-Guides <subsubsec-howto-connect>`.
 		)")
+	    .property<stages::Connect::MergeMode>("merge_mode", "Defines the merge strategy to use")
+	    .property<double>("max_distance", "maximally accepted distance between end and goal sate")
 	    .def(py::init<const std::string&, const Connect::GroupPlannerVector&>(),
 	         "name"_a = std::string("connect"), "planners"_a);