Create custom exceptions in _rclpy.c

[mikaelarguedas]

For now every failure in rclpy raises a RuntimeError, we should create custom errors for different failure scenarios and avoid the tests of just catching random RuntimeErrors.

[suab321321]

@mikaelarguedas I would like to like to contribute

[mikaelarguedas]

@suab321321 I haven't been involved in this project for a long time so can't provide feedback about the status / relevance of this ticket with respect to the current code base.
Maybe current maintainers will be able to provide more up-to-date information.

[jacobperron]

It looks like we have a few custom exceptions defined already:

rclpy/rclpy/src/rclpy/_rclpy.c

Lines 43 to 45 in d375c84

	static PyObject * RCLInvalidROSArgsError;
	static PyObject * UnknownROSArgsError;
	static PyObject * NodeNameNonExistentError;

But a quick search yields several places in _rclpy.c that raise RuntimeError where we might consider using custom exceptions. Whenever a call to the rcl layer errors, at the very least we could return a generic RCLError exception (I think this is what rclcpp does).

@suab321321 If you'd like to contribute to this ticket, I think a good first step would be to replace instances of RuntimeError with a new RCLError whenever there's a failed call to the rcl layer.
I suggest reviewing documentation on writing C-extensions for Python, in particular this section on errors and exceptions. You can add logic to initialize the new exception next to the other exceptions:

rclpy/rclpy/src/rclpy/_rclpy.c

Lines 5088 to 5099 in d375c84

	RCLInvalidROSArgsError = PyErr_NewExceptionWithDoc(
	"_rclpy.RCLInvalidROSArgsError",
	"Thrown when invalid ROS arguments are found by rcl.",
	PyExc_RuntimeError, NULL);
	if (NULL == RCLInvalidROSArgsError) {
	Py_DECREF(m);
	return NULL;
	}
	if (PyModule_AddObject(m, "RCLInvalidROSArgsError", RCLInvalidROSArgsError) != 0) {
	Py_DECREF(m);
	return NULL;
	}

[suab321321]

@jacobperron okay sir I will proceed with this

[suab321321]

@jacobperron sir I have to make RCLError first right?

[jacobperron]

I have to make RCLError first right?

Correct. You can declare and initialize it in the two places of the code I referenced (#31 (comment)).

[suab321321]

#478 here @jacobperron sir