Scene.wait (and .pause) calls add an empty Mobject to self.mobjects

[kjlubick]

Description of bug / unexpected behavior

After each call to Scene's pause() method, I notice a mobject being added to the scene.

class PauseMobjects(Scene):
    def construct(self):
        print(self.mobjects)
        yellow = Square()

        self.play(FadeIn(yellow))
        print(self.mobjects)

        for i in range(0, 5):
            self.pause()
            print(self.mobjects)

Console while running above:

[]
[Square]
[Square, Mobject]
[Square, Mobject, Mobject]
[Square, Mobject, Mobject, Mobject]
[Square, Mobject, Mobject, Mobject, Mobject]
[Square, Mobject, Mobject, Mobject, Mobject, Mobject]
[Square, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject]
[Square, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject]
[Square, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject]
[Square, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject]
[Square, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject, Mobject]

Nothing is rendered here, but I worry that these excess mobjects could be reducing performance, especially because hasing the scene is O(n) where n is the number of mobjects in the scene (e.g. #2710 )

Expected behavior

I would not expect pausing or otherwise waiting to change the mobjects in the scene. From what I've poked around, it's not apparent to me that adding a Mobject is important for waits, so hopefully this can be removed.

Discussion

I am working on a fix, trying to figure out where this mobject is added and prevent that, or at least make sure the mobject is cleaned up after the animation finishes.

This is with v0.16.0

[kjlubick]

Of note, this is with the Cairo renderer, which may be important as I'm figuring out where the mobject is coming from.

[kjlubick]

With the fix in #3041, the console now looks like:

[]
[Square]                                                                                                                                                           
[Square]
[Square]
[Square]
[Square]
[Square]
...

as I would expect.

[huguesdevimeux]

Hello and thanks for the report !

This issue is a long date known issue, there is already one there #1524. I'm closing #1524 in favor of this one, more documented and with a PR attached.

[huguesdevimeux]

Note : the fix proposed by @AntonBallmaier in its original issue looks like a very clean way to do it. No idea wether it would work

[kjlubick]

I also tried "simply passing Wait the remover=True keyword", but that did not work. It appears the Wait animation is not cleaned up in the same way as other animations because it is special-cased in several places.