add resolved_name() method to Publisher about rclpy HOT 7 CLOSED

Hi, community. Do we have any detailed thoughts or designs on this feature? I would like to help

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@crystaldust thanks for taking it up!

I think @dirk-thomas is asking for a method to get the name of a publisher after all remap rules have been applied. I think that means adding a resolved_name() method to the publisher class that internally calls the C function rcl_publisher_get_topic_name(). It will need a method added to the rclpy CPython extension. I think rclpy_get_publisher_logger_Name() would be a good function that could be studied/copied/adapted for this.

• rclpy/rclpy/src/rclpy/_rclpy.c

  Lines 5443 to 5446 in 044ff46

  	{
  	"rclpy_get_publisher_logger_name", rclpy_get_publisher_logger_name, METH_VARARGS,
  	"Get the logger name associated with the node of a publisher."
  	},

• rclpy/rclpy/src/rclpy/_rclpy.c

  Lines 919 to 946 in 044ff46

  	/// Get the name of the logger associated with the node of the publisher.
  	/**
  	* Raises ValueError if pypublisher is not a publisher capsule
  	*
  	* \param[in] pypublisher Capsule pointing to the publisher to get the logger name of
  	* \return logger_name, or
  	* \return None on failure
  	*/
  	static PyObject *
  	rclpy_get_publisher_logger_name(PyObject * Py_UNUSED(self), PyObject * args)
  	{
  	PyObject * pypublisher;
  	if (!PyArg_ParseTuple(args, "O", &pypublisher)) {
  	return NULL;
  	}
  	rclpy_publisher_t * pub = rclpy_handle_get_pointer_from_capsule(pypublisher, "rclpy_publisher_t");
  	if (NULL == pub) {
  	return NULL;
  	}
  	const char * node_logger_name = rcl_node_get_logger_name(pub->node);
  	if (NULL == node_logger_name) {
  	Py_RETURN_NONE;
  	}
  	return PyUnicode_FromString(node_logger_name);
  	}

Though, that doesn't show the final pure-python step. For that you can look at assert_livelines():

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Thanks @sloretz ! I'll look into the code and try, the info is really helpful.

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Hi, @sloretz , I've made a basic implementation on the resolved_name method to call rcl_publisher_get_topic_name(), code here.

Btw, I made a test to run a node with remapping rules calling ros2 run PKG_NAME EXECUTABLE_NAME --ros-args -r FROM:=TO on topics, it also works.

I see there is a ros2 component design, as I understand, the component is a specific node which is loaded into a container and can receive the remapping rules at runtime, but I'm not able to find some rclpy examples to test it, for now, there is only a composition example which is in cpp and calls a RCLCPP_COMPONENTS_REGISTER_NODE macro, and I can't find equivelent things on rclpy project. But the container/component mechanism seems to be implemented in rcl, topic names are updated in rcl lib when the remapping rules are being applied, so calling rcl_publisher_get_topic_name should always work. Is there some demos for rclpy component that I can work with to make a test?

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Hi, @sloretz , I've made a basic implementation on the resolved_name method to call rcl_publisher_get_topic_name(), code here.

Fantastic 🎉

Mind opening a pull request? Then I will be able to use Github's UI to give feedback :)

Is there some demos for rclpy component that I can work with to make a test?

Not that I'm aware of. You're right there is a design for composition that was designed to allow composing Python nodes, but I don't think anyone has written a Python composable node container.

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I've opened the PR #568

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Fixed by @crystaldust in #568 🎉

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