[Python-ideas] A mutable alternative to namedtuple

[Eric Snow]

On Tue, Mar 17, 2015 at 10:52 AM, Luciano Ramalho <luciano at ramalho.org> wrote:
> Sometimes we need a simple class to hold some mutable attributes,
> provide a nice repr, support == for testing, and support iterable
> unpacking, so you can write:
>
>>>> p = Point(3, 4)
>>>> x, y = p
>
> That's very much like the classes built by namedtuple, but mutable.
>
> I propose we add to the collections module another class factory. I am
> calling it plainclass, but perhaps we can think of a better name. Here
> is how it would be used:
>
>>>> import collections
>>>> Point = collections.plainclass('Point', 'x y')
>
> The signature of the plainclass function would be exactly the same as
> namedtuple, supporting the same alternative ways of naming the
> attributes.
>
> The semantics of the generated Point class would be like this code:
>
> https://gist.github.com/ramalho/fd3d367e9d3b2a659faf

Should it also have all the same methods as a namedtuple class (e.g.
the tuple methods, _make, _replace)?  What about the other namedtuple
attrs (_fields, etc.)?

What's the motivation for parity with namedtuple (particularly
iteration)?  I suppose I see the desire for a fixed set of mutable
attributes specific to the generated type.  However, there have been
numerous discussions on this list about alternative approaches to
namedtuple which apply here.  Simply adapting namedtuple may not be
the right thing.

Regardless, this is the sort of thing that should bake outside the
stdlib for a while to prove it's approach and its worth, much as
namedtuple did.  It would also help if there were a concrete use case
in the stdlib that this new class (factory) would satisfy.

> PS. I am aware that there are "Namespace" classes in the standard
> library (e.g. [2]). They solve a different problem.
>
> [2] https://docs.python.org/3/library/argparse.html#argparse.Namespace

Don't forget types.SimpleNamespace. :)

-eric