Death to tuples!

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    Mike> Tuples have the problem that they are immutable, except when
    Mike> they're not (or for proper values of immutable, your
    Mike> choice). They're hashable, except when they're not. Or
    Mike> equivalently, they can be used as dictionary keys - or set
    Mike> elements - except when they can't.

For those of us not following this thread closely, can you identify cases
where tuples are mutable, not hashable or can't be used as dictionary keys?
I've never encountered any such cases.

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