Added Docstring/Example for :meth:always_redraw

manim/animation/updaters/mobject_update_utils.py

@@ -15,6 +15,7 @@
 
 
 import inspect
+from collections.abc import Callable
 
 import numpy as np
 
@@ -55,9 +56,33 @@ def updater(mob):
     return mobject
 
 
-def always_redraw(func):
+def always_redraw(func: Callable[[], Mobject]):
+    """Redraw a mobject every frame.
+
+    .. manim:: TangentAnimation
+
+        class TangentAnimation(Scene):
+            def construct(self):
+                ax = Axes()
+                sine = ax.plot(np.sin, color=RED)
+                alpha = ValueTracker(0)
+                point = always_redraw(
+                        lambda: Dot(
+                            sine.point_from_proportion(alpha.get_value()),
+                            color=BLUE)
+                    )
+                tangent = always_redraw(
+                    lambda: TangentLine(
+                        sine,
+                        alpha=alpha.get_value(),
+                        color=YELLOW,
+                        length=4)
+                )
+                self.add(ax, sine, point, tangent)
+                self.play(alpha.animate.set_value(1), rate_func=linear, run_time=2)
+    """
     mob = func()
-    mob.add_updater(lambda m: mob.become(func()))
+    mob.add_updater(lambda _: mob.become(func()))
     return mob