Add Tree.get_node_by_id

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Added `TreeNode.parent` -- a read-only property for accessing a node's parent https://github.com/Textualize/textual/issues/1397
 - Added public `TreeNode` label access via `TreeNode.label` https://github.com/Textualize/textual/issues/1396
 - Added read-only public access to the children of a `TreeNode` via `TreeNode.children` https://github.com/Textualize/textual/issues/1398
+- Added `Tree.get_node_by_id` to allow getting a node by its ID https://github.com/Textualize/textual/pull/1535
 - Added a `Tree.NodeHighlighted` message, giving a `on_tree_node_highlighted` event handler https://github.com/Textualize/textual/issues/1400
 
 ### Changed

src/textual/widgets/_tree.py

@@ -515,6 +515,26 @@ def get_node_at_line(self, line_no: int) -> TreeNode[TreeDataType] | None:
         else:
             return line.node
 
+    class UnknownID(Exception):
+        """Exception raised when referring to an unknown `TreeNode` ID."""
+
+    def get_node_by_id(self, node_id: NodeID) -> TreeNode[TreeDataType]:
+        """Get a tree node by its ID.
+
+        Args:
+            node_id (NodeID): The ID of the node to get.
+
+        Returns:
+            TreeNode[TreeDataType]: The node associated with that ID.
+
+        Raises:
+            Tree.UnknownID: Raised if the `TreeNode` ID is unknown.
+        """
+        try:
+            return self._nodes[node_id]
+        except KeyError:
+            raise self.UnknownID(f"Unknown TreeNode ID: {node_id}") from None
+
     def validate_cursor_line(self, value: int) -> int:
         """Prevent cursor line from going outside of range."""
         return clamp(value, 0, len(self._tree_lines) - 1)

tests/tree/test_tree_get_node_by_id.py

@@ -0,0 +1,16 @@
+import pytest
+from typing import cast
+from textual.widgets import Tree
+from textual.widgets._tree import NodeID
+
+
+def test_get_tree_node_by_id() -> None:
+    """It should be possible to get a TreeNode by its ID."""
+    tree = Tree[None]("Anakin")
+    child = tree.root.add("Leia")
+    grandchild = child.add("Ben")
+    assert tree.get_node_by_id(tree.root.id).id == tree.root.id
+    assert tree.get_node_by_id(child.id).id == child.id
+    assert tree.get_node_by_id(grandchild.id).id == grandchild.id
+    with pytest.raises(Tree.UnknownID):
+        tree.get_node_by_id(cast(NodeID, grandchild.id + 1000))