Skip to content

MLC102: Scene.play argument cannot be converted to an Animation

qual reports MLC102 when a positional argument of a confirmed Scene.play call is known not to be convertible into an animation:

  • the result of a fluent mobject mutator (mob.shift(...) mutates immediately and returns the mobject itself — the classic bug),
  • a freshly constructed bare mobject (play(Square())),
  • a name known to hold a bare mobject,
  • a numeric or string literal.

Scene.play compiles its arguments (DESIGN §3.2): Animation instances pass through, .animate builders become animations, and everything else raises TypeError at render time.

  • Default severity: error
  • Minimum confidence: high
  • Implementation phase: 1
  • Fix: rewriting mob.method(args) to mob.animate.method(args) is offered as an UNSAFE suggestion for single fluent calls

.animate chains, arguments resolving to Animation classes, and unknown values never fire.

Wrong

class Demo(Scene):
    def construct(self):
        square = Square()
        self.play(square.shift(RIGHT))
        self.play(square)

class Demo(Scene):
    def construct(self):
        square = Square()
        self.play(square.animate.shift(RIGHT))
        self.play(FadeIn(square))