easy question on parsing python: "is not None"

[wheres pythonmonks]

How does "x is not None" make any sense?  "not x is None" does make sense.

I can only surmise that in this context (preceding is) "not" is not a
unary right-associative operator, therefore:

x is not None === IS_NOTEQ(X, None)

Beside "not in" which seems to work similarly, is there other
syntactical sugar like this that I should be aware of?

W