Why are tuples immutable?

[jfj]

Yo.

Why can't we __setitem__ for tuples?
The way I see it is that if we enable __setitem__ for tuples there
doesn't seem to be any performance penalty if the users don't use it
(aka, python performance independent of tuple mutability).

On the other hand, right now we have to use a list if we want to
__setitem__ on a sequence. If we could use tuples in the cases where
we want to modify items but not modify the length of the sequence,
programs could be considerably faster. Yes?

Enlighten me.

G.