more efficient order styles

Author: willmcgugan

src/textual/css/stylesheet.py

@@ -482,7 +482,10 @@ def apply(
         node._has_hover_style = "hover" in all_pseudo_classes
         node._has_focus_within = "focus-within" in all_pseudo_classes
         node._has_order_style = not all_pseudo_classes.isdisjoint(
-            {"first-of-type", "last-of-type", "odd", "even"}
+            {"first-of-type", "last-of-type"}
+        )
+        node._has_odd_or_even = (
+            "odd" in all_pseudo_classes or "even" in all_pseudo_classes
         )
 
         cache_key: tuple | None = None

src/textual/demo/widgets.py

@@ -775,10 +775,9 @@ class WidgetsScreen(PageScreen):
     WidgetsScreen { 
         align-horizontal: center;
         Markdown { background: transparent; }
-        & > VerticalScroll {
+        #container {
             scrollbar-gutter: stable;
-            &> * {            
-              
+            & > * {                          
                 &:even { background: $boost; }
                 padding-bottom: 1;
             }
@@ -789,7 +788,7 @@ class WidgetsScreen(PageScreen):
     BINDINGS = [Binding("escape", "blur", "Unfocus any focused widget", show=False)]
 
     def compose(self) -> ComposeResult:
-        with lazy.Reveal(containers.VerticalScroll(can_focus=True)):
+        with lazy.Reveal(containers.VerticalScroll(id="container", can_focus=True)):
             yield Markdown(WIDGETS_MD, classes="column")
             yield Buttons()
             yield Checkboxes()

src/textual/dom.py

@@ -223,6 +223,8 @@ def __init__(
         self._has_focus_within: bool = False
         self._has_order_style: bool = False
         """The node has an ordered dependent pseudo-style (`:odd`, `:even`, `:first-of-type`, `:last-of-type`)"""
+        self._has_odd_or_even: bool = False
+        """The node has the pseudo class `odd` or `even`."""
         self._reactive_connect: (
             dict[str, tuple[MessagePump, Reactive[object] | object]] | None
         ) = None

src/textual/timer.py

@@ -177,6 +177,11 @@ async def _run(self) -> None:
 
     async def _tick(self, *, next_timer: float, count: int) -> None:
         """Triggers the Timer's action: either call its callback, or sends an event to its target"""
+
+        app = active_app.get()
+        if app._exit:
+            return
+
         if self._callback is not None:
             try:
                 await invoke(self._callback)
@@ -185,7 +190,6 @@ async def _tick(self, *, next_timer: float, count: int) -> None:
                 # Re-raise CancelledErrors that would be caught by the following exception block in Python 3.7
                 raise
             except Exception as error:
-                app = active_app.get()
                 app._handle_exception(error)
         else:
             event = events.Timer(

src/textual/widget.py

@@ -1253,11 +1253,18 @@ def mount(
             parent, *widgets, before=insert_before, after=insert_after
         )
 
-        def update_styles(children: Iterable[DOMNode]) -> None:
+        def update_styles(children: list[DOMNode]) -> None:
             """Update order related CSS"""
-            for child in children:
-                if child._has_order_style:
-                    child._update_styles()
+            if before is not None or after is not None:
+                # If the new children aren't at the end.
+                # we need to update both odd/even and first-of-type/last-of-type
+                for child in children:
+                    if child._has_order_style or child._has_odd_or_even:
+                        child._update_styles()
+            else:
+                for child in children:
+                    if child._has_order_style:
+                        child._update_styles()
 
         self.call_later(update_styles, list(self.children))
         await_mount = AwaitMount(self, mounted)