curds: Add a way to get a nodes nth child

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

curds/playlist/node.py

@@ -45,3 +45,8 @@ class PlaylistNode:
 
     def n_children(self):
         return len(self.children)
+
+    def nth_child(self, n):
+        if n < len(self.children):
+            return self.children[n]
+        return None

curds/playlist/test_node.py

@@ -93,6 +93,23 @@ class TestPlaylistNode(unittest.TestCase):
         self.assertEqual(a.next, b)
         self.assertEqual(b.prev, a)
 
+    def test_node_nth_child(self):
+        root = node.PlaylistNode()
+        a = node.PlaylistNode("a")
+        b = node.PlaylistNode("b")
+        c = node.PlaylistNode("c")
+
+        root.append_child(a)
+        root.append_child(b)
+        a.append_child(c)
+
+        self.assertEqual( root.nth_child(0), a)
+        self.assertEqual( root.nth_child(1), b)
+        self.assertIsNone(root.nth_child(2))
+
+        self.assertEqual( a.nth_child(0), c)
+        self.assertIsNone(a.nth_child(1))
+
     def test_node_parent(self):
         root = node.PlaylistNode()
         a = node.PlaylistNode("a")