Fix import statement and usage for rclpy.node.Node

[mikaelarguedas]

node is not imported in __init__.py anymore (ros2/rclpy#147)

Without this change the demos raise:
AttributeError: module 'rclpy' has not attribute 'Node'

Not sure if ros2/rclpy#147 is a long term fix as this mean that anyone inheriting from Node will need to import it explicitly.

[dhood]

The name of the PR suggests to me that we are changing the demos to inherit from node in this PR; for clarity when searching PRs in the future could you simplify it?

[mikaelarguedas]

The name of the PR suggests to me that we are changing the demos to inherit from node in this PR; for clarity when searching PRs in the future could you simplify it?

Sure, do you have a suggestion?

[wjwwood]

Sure, do you have a suggestion?

"Fix import statement and usage for rclpy.node.Node"?

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This is really unfortunate because it adds another line to all of the examples unnecessarily (imo). It is also asymmetric with what we want to do with the C++ API, i.e. we want rclcpp::Node rather than rclcpp::node::Node. I don't understand fully why @dirk-thomas needed to do what he did in ros2/rclpy#147 (comment), but I think it's a step backwards for the usability of the rclpy API.

[mikaelarguedas]

"Fix import statement and usage for rclpy.node.Node"?

Sounds good to me

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This is really unfortunate because it adds another line to all of the examples unnecessarily (imo). It is also asymmetric with what we want to do with the C++ API, i.e. we want rclcpp::Node rather than rclcpp::node::Node. I don't understand fully why @dirk-thomas needed to do what he did in ros2/rclpy#147 (comment), but I think it's a step backwards for the usability of the rclpy API.

Yeah I agree, I'm proposing this fix mostly to get the demos back to a working state but don't think users should have to import this explicitly in the long-term.
I'd like to merge this before next week but can open a follow-up issue to revisit this before the release. How does that sound ?

[wjwwood]

+1 for getting things working again, but we should try to address this before the release I think.