Skip to content

MLC109: empty AnimationGroup / Succession

qual reports MLC109 when AnimationGroup(...) or Succession(...) is constructed with zero positional animation arguments. Keyword arguments such as lag_ratio configure timing but contribute no animations, so the group animates nothing.

Constructing the empty group is not itself an error in Manim 0.20. AnimationGroup.build_animations_with_timings returns early when there are zero members and init_run_time takes max(..., default=0), so the object is built with a run time of 0. Two outcomes follow, and this rule cannot tell which one applies at the construction site:

  • Harmless: the empty group is nested inside a non-empty group, or is a placeholder that a later branch replaces. It contributes nothing and the render succeeds. AnimationGroup() is a common idiom for "no animation here".
  • Fatal: the empty group reaches Scene.play as the whole animation. Scene.validate_run_time rejects a duration of 0 with ValueError and the render aborts.

The finding is therefore a warning at high confidence rather than a certain error. Narrowing it to the provable case — tracking whether the constructed group is played directly — is open work.

  • Default severity: warning
  • Minimum confidence: high
  • Implementation phase: 1
  • Fix: none

Calls with a *args splat are skipped because the splat may supply animations at runtime.

Wrong

class Demo(Scene):
    def construct(self):
        group = AnimationGroup()
        chain = Succession(lag_ratio=0.5)

class Demo(Scene):
    def construct(self):
        square = Square()
        group = AnimationGroup(FadeIn(square), FadeOut(square))
        chain = Succession(FadeIn(square), FadeOut(square), lag_ratio=0.5)