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Clarification on Immutability please

Hi Python-list folk,

I am sure this has been answered many times before, but I need to ask it

Given that the following is valid Python 2.7.10 (when keyboarded into Idle):

mytup = ("q", "w", "e")
mytup = mytup [:2]

and even that the first id(mytup) returns the same address as the second
one, I am left wondering exactly what immutability is.

I am left concluding that mytup is not actually a tuple (even though type
(mytup) tells me that it is).

My only explanation is that mytup is, actually, a pointer to a tuple; the
pointer can't change, but the contents of that pointer (or the data to
which the pointer points) can change.

That said, if I then type

mytup = mytup + ("r", "t")

I find that this third id call returns a different address from the one
returned by the first two.

Somehow, it seems, tuples can be reduced in length (from the far end)
(which is not what I was expecting), but they cannot be extended (which I
can understand).

I am probably confused, ignorant, stupid, or any combination of the above.

Can you please help me become less so?

Many thanks.

Stephen Tucker.