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MLC117: mobject changed between .animate builder creation and play

qual reports MLC117 for a played .animate builder whose live mobject was definitely mutated between the builder's creation and the play that consumes it, or whose generated target was overwritten by a later .animate builder on the same mobject. Reading .animate runs generate_target() immediately (DESIGN §3.2), so the animation targets the stale snapshot.

  • Default severity: warning
  • Minimum confidence: high
  • Implementation phase: 2
  • Fix: none (moving the builder expression into the self.play(...) call is suggested)

Only definite (all-paths) mutations between creation and play fire; a mutation inside a branch, an unknown-target builder, and a builder created directly inside the play call stay silent.

Wrong

class Demo(Scene):
    def construct(self):
        square = Square()
        self.add(square)
        anim = square.animate.shift(RIGHT)
        square.shift(LEFT)      # mutates after the target snapshot
        self.play(anim)

class Demo(Scene):
    def construct(self):
        square = Square()
        self.add(square)
        square.shift(LEFT)      # mutate first
        self.play(square.animate.shift(RIGHT))