feat: set_default for Animation class (#3876)

* feat: Animation.set_default

Adds set_default class method to Animation class based on existing implementation for Mobject class.

Addresses issue #3142

* test: added missing test

* fix: docstring formatting

---------

Co-authored-by: Benjamin Hackl <[email protected]>

Author: christopher-hampson

manim/animation/animation.py

@@ -16,6 +16,7 @@
 
 from collections.abc import Iterable, Sequence
 from copy import deepcopy
+from functools import partialmethod
 from typing import TYPE_CHECKING, Callable
 
 from typing_extensions import Self
@@ -479,6 +480,52 @@ def is_introducer(self) -> bool:
         """
         return self.introducer
 
+    @classmethod
+    def __init_subclass__(cls, **kwargs) -> None:
+        super().__init_subclass__(**kwargs)
+
+        cls._original__init__ = cls.__init__
+
+    @classmethod
+    def set_default(cls, **kwargs) -> None:
+        """Sets the default values of keyword arguments.
+
+        If this method is called without any additional keyword
+        arguments, the original default values of the initialization
+        method of this class are restored.
+
+        Parameters
+        ----------
+
+        kwargs
+            Passing any keyword argument will update the default
+            values of the keyword arguments of the initialization
+            function of this class.
+
+        Examples
+        --------
+
+        .. manim:: ChangeDefaultAnimation
+
+            class ChangeDefaultAnimation(Scene):
+                def construct(self):
+                    Rotate.set_default(run_time=2, rate_func=rate_functions.linear)
+                    Indicate.set_default(color=None)
+
+                    S = Square(color=BLUE, fill_color=BLUE, fill_opacity=0.25)
+                    self.add(S)
+                    self.play(Rotate(S, PI))
+                    self.play(Indicate(S))
+
+                    Rotate.set_default()
+                    Indicate.set_default()
+
+        """
+        if kwargs:
+            cls.__init__ = partialmethod(cls.__init__, **kwargs)
+        else:
+            cls.__init__ = cls._original__init__
+
 
 def prepare_animation(
     anim: Animation | mobject._AnimationBuilder,

tests/test_graphical_units/test_animation.py

@@ -0,0 +1,16 @@
+from manim import *
+from manim.animation.animation import DEFAULT_ANIMATION_RUN_TIME
+
+__module_test__ = "animation"
+
+
+def test_animation_set_default():
+    s = Square()
+    Rotate.set_default(run_time=100)
+    anim = Rotate(s)
+    assert anim.run_time == 100
+    anim = Rotate(s, run_time=5)
+    assert anim.run_time == 5
+    Rotate.set_default()
+    anim = Rotate(s)
+    assert anim.run_time == DEFAULT_ANIMATION_RUN_TIME