Create custom exceptions in _rclpy.c about rclpy HOT 7 CLOSED

#478 here @jacobperron sir

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@mikaelarguedas I would like to like to contribute

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@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.

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

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:

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@jacobperron okay sir I will proceed with this

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@jacobperron sir I have to make RCLError first right?

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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)).

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