Allow Dash children lists to be tuples also.

[rmarren1]

Right now we only accept objects which are instances of collections.MutableSequence as lists in Dash.

Is there a reason we are this specific? A tuple will be serialized just fine.

[T4rk1n]

If it serialize, then I see no reason not to accept them.

[chriddyp]

we only accept objects which are instances of collections.MutableSequence as lists in Dash.

By 'only accept', do you mean in the plotly.utils.PlotlyJSONEncoder or in the base_component.Component?

[rmarren1]

PlotlyJSONEncoder looks like it allows tuples.

It looks like the problem is just that the base component traversal uses isinstance(x, collections.MutableSequence) to check if an object is a list here and here and here and here.

I think if we just change these lines to collections.Sequence we should get support for tuples.

[chriddyp]

Yeah, I don't think that we're using any of those extra MutableSequence methods (append, reverse, extend, pop, remove, __iadd__), so I think we're good. (https://docs.python.org/2/library/collections.html#collections-abstract-base-classes)

[rmarren1]

I'll make a PR and see how it works out

[rmarren1]

It turns out making Dash children a tuple instead of a list (e.g. html.Div(children=(html.P("Hello"), html.P("World"))) already works, but the Component.traverse() method does not work correctly in these instances so some things break like layout validation, JSON serializable error checking, etc

[rmarren1]

strings are instances of collections.Sequence, so to get the desired behavior I just added tuple to the list of accepted types, e.g. isinstance(x, (tuple, collections.MutableMapping)) instead of isinstance(x, collections.MutableMapping)