Mobject.remove() repeatedly checks for list membership

[leotrs]

This is a fairly edge-case optimization, so please feel free to close this if it's deemed to niche.

Currently, the definition of Mobject.remove does this:

    def remove(self, *mobjects):
        for mobject in mobjects:
            if mobject in self.submobjects:
                self.submobjects.remove(mobject)
        return self

At each removed mobject, the code mobject in self.submobjects is executed and performs linear search over a list, which is far from optimal if self.submobjects is large (even if mobjects is small). It would be more efficient to use an object that allows for O(1) membership checks, like a dict or a set (or an OrderedDict).

[huguesdevimeux]

I guess that there is no case of purposeful duplicate within self.submobjects, as if we use set they will be deleted.

[leotrs]

On the one hand, there are no repeated Mobjects in a scene, Scene.mobjects could be a set, not a lost. On the other hand, the code originally used the position of each Mobject in that list to determine the drawing order. But now that is done via Mobject.z_index.

So, in principle, I think we could change Scene.mobjects to be a set, and delete a while bunch of legacy code. Can anyone think of objections?

[leotrs]

We are thinking of not using z_index anymore, so my last comment doesn't work anymore.

On the topic of this issue: I think there are deeper refactorings to be done with submobjects (#358), so whatever is done to fix the present issues would be temporary at best. Closing for now.