Correct. Except that, the examples you used would be true no matter how my extension worked, because that's how Python lists work.

The thing that I have some control over (and have decided to mimic the way lists work) is when getting cmplex members from my other new types...

norm = tripoly.normal
norm += vec                      # <-- just altered what's in tripoly.normal

norm = tripoly.normal.Clone()
norm += vec                      # <-- did not alter what's in tripoly.normal

...if in doubt, my suggestion is to fire up the stand-alone interpreter and do some tests (with lists, as in my docs, as well).

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