Query dom - get child

sandbox/local_styles.py

@@ -1,7 +1,7 @@
-from textual.app import App
 from textual import events
-from textual.widgets import Placeholder
+from textual.app import App
 from textual.widget import Widget
+from textual.widgets import Placeholder
 
 
 class BasicApp(App):
@@ -20,14 +20,17 @@ class BasicApp(App):
         await self.dispatch_key(event)
 
     def key_a(self) -> None:
-        self.query("#footer").set_styles(text="on magenta")
+        footer = self.get_child("#footer")
+        footer.set_styles(text="on magenta")
 
     def key_b(self) -> None:
-        self["#footer"].set_styles("text: on green")
+        footer = self.get_child("#footer")
+        footer.set_styles("text: on green")
 
     def key_c(self) -> None:
-        self["#header"].toggle_class("-highlight")
-        self.log(self["#header"].styles)
+        header = self.get_child("#header")
+        header.toggle_class("-highlight")
+        self.log(header.styles)
 
 
 BasicApp.run(css_file="local_styles.css", log="textual.log")

src/textual/app.py

@@ -36,7 +36,7 @@ from .reactive import Reactive
 from .view import View
 from .widget import Widget
 
-from .css.query import EmptyQueryError
+from .css.query import NoMatchingNodesError
 
 if TYPE_CHECKING:
     from .css.query import DOMQuery
@@ -279,13 +279,18 @@ class App(DOMNode):
 
         return DOMQuery(self.view, selector)
 
-    def __getitem__(self, selector: str) -> DOMNode:
-        from .css.query import DOMQuery
+    def get_child(self, selector: str) -> DOMNode:
+        """Shorthand for self.view.get_child(selector: str)
+        Returns the first child (immediate descendent) of this DOMNode
+        matching the selector.
 
-        try:
-            return DOMQuery(self.view, selector).first()
-        except EmptyQueryError:
-            raise KeyError(selector)
+        Args:
+            selector (str): A CSS selector.
+
+        Returns:
+            DOMNode: The first child of this node which matches the selector.
+        """
+        return self.view.get_child(selector)
 
     def update_styles(self) -> None:
         """Request update of styles.

src/textual/css/query.py

@@ -26,7 +26,7 @@ if TYPE_CHECKING:
     from ..dom import DOMNode
 
 
-class EmptyQueryError(Exception):
+class NoMatchingNodesError(Exception):
     pass
 
 
@@ -38,7 +38,7 @@ class DOMQuery:
         selector: str | None = None,
         nodes: list[DOMNode] | None = None,
     ) -> None:
-
+        self._selector = selector
         self._nodes: list[DOMNode] = []
         if nodes is not None:
             self._nodes = nodes
@@ -103,7 +103,9 @@ class DOMQuery:
         if self._nodes:
             return self._nodes[0]
         else:
-            raise EmptyQueryError("Query is empty")
+            raise NoMatchingNodesError(
+                f"No nodes match the selector {self._selector!r}"
+            )
 
     def add_class(self, *class_names: str) -> DOMQuery:
         """Add the given class name(s) to nodes."""

src/textual/dom.py

@@ -282,6 +282,20 @@ class DOMNode(MessagePump):
                 if node.children:
                     push(iter(node.children))
 
+    def get_child(self, selector: str) -> DOMNode:
+        """Return the first child (immediate descendent) of this DOMNode matching a selector.
+
+        Args:
+            selector (str): A CSS selector.
+
+        Returns:
+            DOMNode: The first child of this node which matches the selector.
+        """
+        from .css.query import DOMQuery
+
+        query = DOMQuery(selector=selector, nodes=list(self.children))
+        return query.first()
+
     def query(self, selector: str | None = None) -> DOMQuery:
         """Get a DOM query.
 

src/textual/view.py

@@ -69,12 +69,6 @@ class View(Widget):
     def __rich_repr__(self) -> rich.repr.Result:
         yield "name", self.name
 
-    def __getitem__(self, widget_id: str) -> Widget:
-        try:
-            return self.get_child_by_id(widget_id)
-        except errors.MissingWidget as error:
-            raise KeyError(str(error))
-
     @property
     def is_visual(self) -> bool:
         return False

tests/test_dom.py

@@ -1,6 +1,7 @@
 import pytest
 
 from textual.css.errors import StyleValueError
+from textual.css.query import NoMatchingNodesError
 from textual.dom import DOMNode
 
 
@@ -23,3 +24,38 @@ def test_display_set_invalid_value():
     node = DOMNode()
     with pytest.raises(StyleValueError):
         node.display = "blah"
+
+
+@pytest.fixture
+def parent():
+    parent = DOMNode(id="parent")
+
+    child1 = DOMNode(id="child1")
+    child1.add_class("foo")
+    child2 = DOMNode(id="child2")
+    child2.add_class("bar")
+
+    grandchild1 = DOMNode(id="grandchild1")
+    child1.add_child(grandchild1)
+
+    parent.add_child(child1)
+    parent.add_child(child2)
+
+    yield parent
+
+
+def test_get_child_gets_first_child(parent):
+    child = parent.get_child(".foo")
+    assert child.id == "child1"
+    assert child.get_child("#grandchild1").id == "grandchild1"
+    assert parent.get_child(".bar").id == "child2"
+
+
+def test_get_child_no_matching_child(parent):
+    with pytest.raises(NoMatchingNodesError):
+        parent.get_child("#doesnt-exist")
+
+
+def test_get_child_only_immediate_descendents(parent):
+    with pytest.raises(NoMatchingNodesError):
+        parent.get_child("#grandchild1")