Add read-only access to the children of a TreeNode

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 
 - 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
 
 ### Changed
 

src/textual/_immutable_sequence_view.py

@@ -0,0 +1,68 @@
+"""Provides an immutable sequence view class."""
+
+from __future__ import annotations
+from sys import maxsize
+from typing import Generic, TypeVar, Iterator, overload, Sequence
+
+T = TypeVar("T")
+
+
+class ImmutableSequenceView(Generic[T]):
+    """Class to wrap a sequence of some sort, but not allow modification."""
+
+    def __init__(self, wrap: Sequence[T]) -> None:
+        """Initialise the immutable sequence.
+
+        Args:
+            wrap (Sequence[T]): The sequence being wrapped.
+        """
+        self._wrap = wrap
+
+    @overload
+    def __getitem__(self, index: int) -> T:
+        ...
+
+    @overload
+    def __getitem__(self, index: slice) -> ImmutableSequenceView[T]:
+        ...
+
+    def __getitem__(self, index: int | slice) -> T | ImmutableSequenceView[T]:
+        return (
+            self._wrap[index]
+            if isinstance(index, int)
+            else ImmutableSequenceView[T](self._wrap[index])
+        )
+
+    def __iter__(self) -> Iterator[T]:
+        return iter(self._wrap)
+
+    def __len__(self) -> int:
+        return len(self._wrap)
+
+    def __length_hint__(self) -> int:
+        return len(self)
+
+    def __bool__(self) -> bool:
+        return bool(self._wrap)
+
+    def __contains__(self, item: T) -> bool:
+        return item in self._wrap
+
+    def index(self, item: T, start: int = 0, stop: int = maxsize) -> int:
+        """Return the index of the given item.
+
+        Args:
+            item (T): The item to find in the sequence.
+            start (int, optional): Optional start location.
+            stop (int, optional): Optional stop location.
+
+        Returns:
+            T: The index of the item in the sequence.
+
+        Raises:
+            ValueError: If the item is not in the sequence.
+        """
+        return self._wrap.index(item, start, stop)
+
+    def __reversed__(self) -> Iterator[T]:
+        return reversed(self._wrap)

src/textual/widgets/_tree.py

@@ -14,6 +14,7 @@
 from .._segment_tools import line_crop, line_pad
 from .._types import MessageTarget
 from .._typing import TypeAlias
+from .._immutable_sequence_view import ImmutableSequenceView
 from ..binding import Binding
 from ..geometry import Region, Size, clamp
 from ..message import Message
@@ -53,6 +54,10 @@ def _get_guide_width(self, guide_depth: int, show_root: bool) -> int:
         return guides
 
 
+class TreeNodes(ImmutableSequenceView["TreeNode[TreeDataType]"]):
+    """An immutable collection of `TreeNode`."""
+
+
 @rich.repr.auto
 class TreeNode(Generic[TreeDataType]):
     """An object that represents a "node" in a tree control."""
@@ -74,7 +79,7 @@ def __init__(
         self._label = tree.process_label(label)
         self.data = data
         self._expanded = expanded
-        self._children: list[TreeNode] = []
+        self._children: list[TreeNode[TreeDataType]] = []
 
         self._hover_ = False
         self._selected_ = False
@@ -91,6 +96,11 @@ def _reset(self) -> None:
         self._selected_ = False
         self._updates += 1
 
+    @property
+    def children(self) -> TreeNodes[TreeDataType]:
+        """TreeNodes[TreeDataType]: The child nodes of a TreeNode."""
+        return TreeNodes(self._children)
+
     @property
     def line(self) -> int:
         """int: Get the line number for this node, or -1 if it is not displayed."""

tests/test_immutable_sequence_view.py

@@ -0,0 +1,68 @@
+import pytest
+
+from typing import Sequence
+from textual._immutable_sequence_view import ImmutableSequenceView
+
+def wrap(source: Sequence[int]) -> ImmutableSequenceView[int]:
+    """Wrap a sequence of integers inside an immutable sequence view."""
+    return ImmutableSequenceView[int](source)
+
+
+def test_empty_immutable_sequence() -> None:
+    """An empty immutable sequence should act as anticipated."""
+    assert len(wrap([])) == 0
+    assert bool(wrap([])) is False
+    assert list(wrap([])) == []
+
+
+def test_non_empty_immutable_sequence() -> None:
+    """A non-empty immutable sequence should act as anticipated."""
+    assert len(wrap([0])) == 1
+    assert bool(wrap([0])) is True
+    assert list(wrap([0])) == [0]
+
+
+def test_no_assign_to_immutable_sequence() -> None:
+    """It should not be possible to assign into an immutable sequence."""
+    tester = wrap([1,2,3,4,5])
+    with pytest.raises(TypeError):
+        tester[0] = 23
+    with pytest.raises(TypeError):
+        tester[0:3] = 23
+
+
+def test_no_del_from_iummutable_sequence() -> None:
+    """It should not be possible delete an item from an immutable sequence."""
+    tester = wrap([1,2,3,4,5])
+    with pytest.raises(TypeError):
+        del tester[0]
+
+
+def test_get_item_from_immutable_sequence() -> None:
+    """It should be possible to get an item from an immutable sequence."""
+    assert wrap(range(10))[0] == 0
+    assert wrap(range(10))[-1] == 9
+
+
+def test_get_slice_from_immutable_sequence() -> None:
+    """It should be possible to get a slice from an immutable sequence."""
+    assert list(wrap(range(10))[0:2]) == [0,1]
+    assert list(wrap(range(10))[0:-1]) == [0,1,2,3,4,5,6,7,8]
+
+
+def test_immutable_sequence_contains() -> None:
+    """It should be possible to see if an immutable sequence contains a value."""
+    tester = wrap([1,2,3,4,5])
+    assert 1 in tester
+    assert 11 not in tester
+
+
+def test_immutable_sequence_index() -> None:
+    tester = wrap([1,2,3,4,5])
+    assert tester.index(1) == 0
+    with pytest.raises(ValueError):
+        _ = tester.index(11)
+
+
+def test_reverse_immutable_sequence() -> None:
+    assert list(reversed(wrap([1,2]))) == [2,1]

tests/tree/test_tree_node_children.py

@@ -0,0 +1,27 @@
+import pytest
+from textual.widgets import Tree, TreeNode
+
+def label_of(node: TreeNode[None]):
+    """Get the label of a node as a string"""
+    return str(node.label)
+
+
+def test_tree_node_children() -> None:
+    """A node's children property should act like an immutable list."""
+    CHILDREN=23
+    tree = Tree[None]("Root")
+    for child in range(CHILDREN):
+        tree.root.add(str(child))
+    assert len(tree.root.children)==CHILDREN
+    for child in range(CHILDREN):
+        assert label_of(tree.root.children[child]) == str(child)
+    assert label_of(tree.root.children[0]) == "0"
+    assert label_of(tree.root.children[-1]) == str(CHILDREN-1)
+    assert [label_of(node) for node in tree.root.children] == [str(n) for n in range(CHILDREN)]
+    assert [label_of(node) for node in tree.root.children[:2]] == [str(n) for n in range(2)]
+    with pytest.raises(TypeError):
+        tree.root.children[0] = tree.root.children[1]
+    with pytest.raises(TypeError):
+        del tree.root.children[0]
+    with pytest.raises(TypeError):
+        del tree.root.children[0:2]