Add an insert method to the NodeList

src/textual/_node_list.py

@@ -64,6 +64,17 @@ class NodeList(Sequence):
             self._nodes_set.add(widget)
             self._updates += 1
 
+    def _insert(self, index: int, widget: Widget) -> None:
+        """Insert a Widget.
+
+        Args:
+            widget (Widget): A widget.
+        """
+        if widget not in self._nodes_set:
+            self._nodes.insert(index, widget)
+            self._nodes_set.add(widget)
+            self._updates += 1
+
     def _remove(self, widget: Widget) -> None:
         """Remove a widget from the list.
 

tests/test_node_list.py

@@ -21,6 +21,16 @@ def test_repeat_add_one():
         nodes._append(widget)
     assert len(nodes)==1
 
+def test_insert():
+    nodes = NodeList()
+    widget1 = Widget()
+    widget2 = Widget()
+    widget3 = Widget()
+    nodes._append(widget1)
+    nodes._append(widget3)
+    nodes._insert(1,widget2)
+    assert list(nodes) == [widget1,widget2,widget3]
+
 def test_truthy():
     """Does a node list act as a truthy object?"""
     nodes = NodeList()