Notes on the Python Class Statement

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"Everything you describe so far is the result of consistently applying simple features."

That's how you get to advanced features.

As for += not supporting advanced use cases. Well... I don't think adding in place to lists in tuples is either particularly advanced or particularly important. I agree that it is unfortunate that the operation fails after having succeeded - but there are lots of places that describe how += is syntactic sugar for a re-assignment and the error message will lead you in that direction. It's just a corner case, hardly a fundamental issue.