Added docstring and example to update.py

manim/animation/updaters/update.py

@@ -16,10 +16,45 @@
 
 
 class UpdateFromFunc(Animation):
-    """
-    update_function of the form func(mobject), presumably
-    to be used when the state of one mobject is dependent
-    on another simultaneously animated mobject
+    """Updates the mobject based on an update_function of the form func(mobject).
+
+    This can be used when the state of one mobject is dependent
+    on another simultaneously animated mobject.
+
+    Parameters
+    ----------
+    mobject
+        The mobject which needs to be updated.
+
+    update_function
+        The function of the form func(mobject)
+        which would determine how the mobject is getting updated each frame.
+
+    suspend_mobject_updating
+        If ``True``, any updater added via ``add_updater`` on the mobject
+        is suspended for the duration of this animation. Defaults to ``False``.
+
+    **kwargs
+        Any other keyword arguments to be passed to :class:`Animation`.
+
+    Example::
+
+        from manim import *
+
+
+        class UpdateFromFuncDemo(Scene):
+            def construct(self):
+                dot = Dot().to_edge(1.5 * LEFT)
+                label = Text("Hello").next_to(dot, UP)
+
+                def update_func(mob):
+                    mob.next_to(dot, UP)
+
+                self.play(
+                    dot.animate.to_edge(1.5 * RIGHT),
+                    UpdateFromFunc(label, update_func),
+                    run_time=3,
+                )
     """
 
     def __init__(
@@ -39,11 +74,88 @@ def interpolate_mobject(self, alpha: float) -> None:
 
 
 class UpdateFromAlphaFunc(UpdateFromFunc):
+    """Updates the mobject based on an update_function of the form func(mobject, alpha).
+
+    This can be used when the state of one mobject is dependent on:
+    (1) Another simultaneously animated mobject
+    (2) alpha value
+
+    Parameters
+    ----------
+    mobject
+        The mobject which needs to be updated.
+
+    update_function
+        The function of the form func(mobject, alpha)
+        which would determine how the mobject is getting updated each frame.
+
+    suspend_mobject_updating
+        If ``True``, any updater added via ``add_updater`` on the mobject
+        is suspended for the duration of this animation. Defaults to ``False``.
+
+    **kwargs
+        Any other keyword arguments to be passed to :class:`Animation`.
+
+    Example::
+
+        from manim import *
+
+
+        class UpdateFromAlphaFuncDemo(Scene):
+            def construct(self):
+                dot = Dot().to_edge(1.5 * LEFT)
+                label = Text("Hello").next_to(dot, UP)
+                number = DecimalNumber()
+                vg = VGroup(label, number)
+                self.add(vg)
+
+                def update_func(mob, alpha):
+                    m, n = mob
+                    m.next_to(dot, UP)
+                    m.set_opacity(alpha)
+                    n.set_value(alpha).next_to(dot, DOWN)
+
+                self.play(
+                    dot.animate.to_edge(1.5 * RIGHT),
+                    UpdateFromAlphaFunc(vg, update_func),
+                    run_time=3,
+                )
+    """
+
     def interpolate_mobject(self, alpha: float) -> None:
         self.update_function(self.mobject, self.rate_func(alpha))  # type: ignore[call-arg, arg-type]
 
 
 class MaintainPositionRelativeTo(Animation):
+    """Useful when one mobject's position is to be maintained constant w.r.t another mobject's position.
+
+    Parameters
+    ----------
+    mobject
+        The mobject whose position is to be kept constant w.r.t another mobject
+    tracked_mobject
+        This is the mobject w.r.t whose position, the mobject's position is to be kept constant.
+    **kwargs
+        Any other keyword arguments to be passed to :class:`Animation`.
+
+    Example::
+
+        from manim import *
+
+
+        class MaintainPositionRelativeToDemo(Scene):
+            def construct(self):
+                dot = Dot().to_edge(1.5 * LEFT)
+                label = Text("Hello").next_to(dot, UP)
+
+                self.play(
+                    dot.animate.to_edge(1.5 * RIGHT),
+                    MaintainPositionRelativeTo(label, dot),
+                    run_time=3,
+                )
+
+    """
+
     def __init__(
         self, mobject: Mobject, tracked_mobject: Mobject, **kwargs: Any
     ) -> None:
@@ -57,4 +169,4 @@ def __init__(
     def interpolate_mobject(self, alpha: float) -> None:
         target = self.tracked_mobject.get_center()
         location = self.mobject.get_center()
-        self.mobject.shift(target - location + self.diff)
+        self.mobject.shift(target + self.diff - location)