add initial drawing balls from a urn animation

math/combinatorics.py

@@ -0,0 +1,39 @@
+from manim import *
+import random
+
+class Urn(Square):
+    def __init__(self):
+        Square.__init__(self, side_length=1.0, fill_color=GREY, fill_opacity=1.0)
+
+class Balls(VGroup):
+    colors = [BLUE, GREEN, YELLOW, PURPLE, RED, GRAY, MAROON, ORANGE, TEAL]
+
+    def __init__(self, n):
+        cols = Balls.colors
+        random.shuffle(cols)
+        cols = cols[:n]
+        super().__init__(*[LabeledDot(str(l), color=c) for l, c in zip(list(range(n)), cols)])
+
+class Main(Scene):
+    def construct(self):
+
+        urn = Urn().shift(3*LEFT)
+
+        n = 9
+        k = 6
+        balls = Balls(n)
+
+        left = list(range(n))
+        random.shuffle(left)
+        left = left[:k]
+        for d in left:
+
+            self.add(balls[d].move_to(urn), urn)
+            self.play(balls[d].animate.shift(DOWN))
+
+            self.play(urn.animate.shift(RIGHT))
+
+
+        self.wait(2)
+
+