Tuples and immutability

Ian Kelly ian.g.kelly at gmail.com
Sun Mar 2 13:32:35 CET 2014


On Sat, Mar 1, 2014 at 7:04 PM, Eric Jacoboni <eric.jacoboni at gmail.com> wrote:
> In fact, i think i'm gonna forget += on lists :)

Well, do what you want, but I think you're taking the wrong lesson
from this.  Don't forget about using += on lists.  Instead, forget
about using assignments, augmented or otherwise, on tuple elements.
Would you expect this to work?

    tup = (1, 2, 3)
    tup[1] += 42

I'm guessing probably not.  So I have a hard time understanding why it
should be expected to work any differently when the tuple element
happens to be a list.  The fact that the list is actually modified I
think is a distraction from the main point: the error indicates that
something illegal happened, not that nothing has changed.  Assignments
just are not allowed on tuple elements, and it doesn't matter what
type they happen to be.



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