Make mypy happy (#1831)

* Helper file for error progress tracking.

* Fix typing of Keys.???.value.

* Assert that we have frame information.

@willmcgugan I went with the asserts because the tone of the code tells me that we are kind of certain that the current and previous frames always exist. Should the function be refactored to handle None for the previous frame (or the current & previous frames) by writing to the buffer without caller information, for example?

* Use inspect.Traceback instead of inspect.FrameInfo.

Looks like the two shared a lot of attributes, so we were trying to use FrameInfo but inspect.getframeinfo returns a Traceback, so that felt like the correct type to use.

* Update after installing msgpack-types.

* Assert we have frame info.

Same fix as in b709219.

* Fix MapGeometry order information typing.

There was another alternative solution, which was to just flatten everything entirely, so that the code actually obeyed the comments.
After all, the comments for the attribute `order` in the definition of `MapGeometry` said that `order` was a tuple of integers defining the painting order, which was not true because the very first widget was having its order defined as `order = ((0,),)` instead of `order = (0,)`.
Thus, another possible solution would be to retype `order` as `tuple[int, ...]` and make everything flat, but I opted for the “tuple of tuples” approach because the sub-tuples will highlight the nested structure of the DOM hierarchy.

* Fix import and typing for fromkeys.

* Assert app is not None.

[skip cli]

* Import missing type.

* Use CallbackType for event Callback.

* Remove variable name clash.

* Ensure ScalarAnimation only receives widgets.

Two other alternatives would be:
 - leave typing of 'widget: DOMNode' and then assert 'widget' is actually of type 'Widget', which works just fine but looks weird in the sense that we type a parameter in one way but then only manage to do any work if it is of another type;
 - type it as 'widget: DOMNode | Widget' and set 'size' to something other than 'widget.outer_size' if 'widget' is a 'DOMNode'.

* Count spacing values as 1 for int instance.

Adding an 'assert not isinstance(spacing, int)' before raising the error sounds reasonable, because 'Spacing.unpack' seems to be able to handle a lone integer just fine, but I decided against it because I would not like to raise an assertion error from within an exception handling inside Textual.
So, to keep it on the safer side, I went with the conditional expression that checks if we have an integer or a tuple.

* Use correct default.

The obvious fix would be to do 'default_factory=RulesMap' but mypy will infer that the type of 'RulesMap' is 'type[RulesMap]' and will not see it as a 'Callable[[], RulesMap]'. That could be fixed by using 'cast'. I decided to use 'RulesMap.__call__'.

[skip ci]

* Use correct abstract methods.

We fix the LSP violation by using the abstract methods that the ABC already provides... Which is a shame, because I thought I was about to write my first Protocol.

* Add missing annotation.

* Fix type inference.

* Check token is not None.

* Revert "Check token is not None."

This reverts commit 0ae463366e53403aa8cacf7559af889571f382e1.
Upon closer look, this is not the correct fix.

* Check that token is not None.

Checking if the token is not 'None' brings us a tiny step closer to fixing #1849, which still needs to ensure the variable definition is complete and valid, even if empty.

* Type DOMQuery instantiation correctly.

After some fiddling, some crying, and talking to Dave and Will, we got to a partial solution.
I cried a bit more and came up with the fix that entailed lifting 'ExpectType' to outside of 'DOMNode'.
Then, I realised 'ExpectType' and 'QueryType' from 'query.py' were essentially the same thing so I decided to only make use of 'QueryType'.

* Infer correct type while walking.

* Cast to remove doubt about None.

mypy can't infer that if after is None, then before won't.

* Explicitly type variable.

* Cast to console renderable.

@willmcgugan did I understand correctly that this 'cast' is exactly what renderable being possibly a 'RichCast' asks me to do..? To be honest, I was not 100% sure after reading rich's documentation for 'RichCast' and after reading the source of 'rich_cast'.

* Type variable to remove literal ambiguity.

mypy was inferring the type of the empty string as a literal and thus was not type checking the fact that 'render' would either be a string or Text.

* Assert scrollbars always have parents.

* Make scrollbar scroll actions synchronous.

The scrollbars were posting the messages and awaiting for them but that's not what Widget does, which handles scrolling synchronously. Thus, I made them synchronous methods by using 'post_message_no_wait'.

* Use link only when available.

* Update errors.

* Relax type inference.

* Ignore missing imports for uvloop.

'uvloop' is completely optional and this code only exists to cater for the case where the user _already_ has uvloop installed.
With that in mind, it makes sense to silence errors about uvloop not being available because we don't need to know about that.
We only care if uvloop happens to be installed.

* Enable variable reuse.

* Fix type issues in easing.py.

* Fix typing issues in demo.

Fixing the typing issues here involved making use of the messaging features to replace a method (wasn't exactly wrong, but this is more in line with the Textual way of doing things, which should be prevalent in the demo of the framework).
We also dealt with a typing issue in DarkSwitch.on_dark_change by deleting an unnecessary parameter, but the underlying problem is unsolved and was logged as issue #1865.

Related issues: #1865.

* Fix typing issues in _doc.py.

* Type actions with a type alias.

* Make return values optional.

As per discussion with @darrenburns.

* Make StringKey idempotent.

This set up is so that we can easily make sure that a variable of the type str | SK (where SK is a subclass of StringKey) becomes of the type SK.
Instead of having to write a conditional expression to only convert in case of a string, we make SK idempotent so that we can just call it on the value that may still be a string.

* Make sorting type safe.

* Fix typing of StringKey.__new__.

This is needed to ensure the type checkers know the exact type of the instances returned when instantiating subclasses of StringKey.

* Add explicit type variables.

* Type-safe line rendering.

* Type safe _render_line_in_row.

* Type safe _render_cell.

* Type safe ordered_rows property.

* Type safe ordered_columns property.

* Simplify handling of Nones in TwoWayDict.

In the beginning of the work on this PR, mypy flagged two issues in the implementation of TwoWayDict, which would return None when the keys/values were not available but the signatures of get/get_key did not have the missing '| None'.
When I added the '| None' to the return values of TwoWayDict.get and TwoWayDict.get_key, many new errors popped up because the implementation of DataTable assumes, in many different places, that those methods return the exact thing that we asked for, and not None.

To fix this, I started going over the call sites for get/get_key and started adding checks for 'None' and raising the appropriate RowDoesNotExist/ColumnDoesNotExist error.

At some point, I realised that went a little bit against the semantics of the code, which pretty much assumes those accesses WILL work.

So, I subclassed TwoWayDict to specialise it even further to this use case.
The subclass is meant to work with RowKey/ColumnKey as the underlying keys and it will automatically raise an error if the access fails.

CC: @darrenburns.

* Make use of idempotency of StringKey subclasses.

* Make message aware of type of sender.

* Only select when possible.

* Fix typing of reactive attribute.

* Reset cursor upon moving action if needed.

* Assure mypy we have ListItems.

This could be improved (as in, cast wouldn't be needed) if #1871 is resolved favourably.

* Add explicit return.

* Ignore argument types to watch.

Related issues: #1865.

* Type safe App._register.

* Redirect output to void.

* Remove helper file.

* Fix Python compat. issues.

* Button can only accept str/Text as label.

Fixes: #1870.

* Add runtime type check for list items.

This change follows from a discussion in issue #1871.

* Address review comments.

* Revert "Fix typing issues in demo."

This reverts commit f36678392046ae6ffcf1e3e5f8354e91ec5f50f2.

* Address review comments.

Related comments: https://github.com/Textualize/textual/pull/1831\#discussion_r1118155296

* Add clarifying comment.

See: https://github.com/Textualize/textual/pull/1831\#discussion_r1118154777

* Revert changes to data table.

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Changed
 
 - Widget scrolling methods (such as `Widget.scroll_home` and `Widget.scroll_end`) now perform the scroll after the next refresh https://github.com/Textualize/textual/issues/1774
+- Buttons no longer accept arbitrary renderables https://github.com/Textualize/textual/issues/1870
 
 ### Fixed
 

mypy.ini

@@ -14,3 +14,7 @@ ignore_missing_imports = True
 
 [mypy-ipywidgets.*]
 ignore_missing_imports = True
+
+[mypy-uvloop.*]
+# Ignore missing imports for optional library that isn't listed as a dependency.
+ignore_missing_imports = True

src/textual/__init__.py

@@ -64,7 +64,10 @@ class Logger:
         if app.devtools is None or not app.devtools.is_connected:
             return
 
-        previous_frame = inspect.currentframe().f_back
+        current_frame = inspect.currentframe()
+        assert current_frame is not None
+        previous_frame = current_frame.f_back
+        assert previous_frame is not None
         caller = inspect.getframeinfo(previous_frame)
 
         _log = self._log or app._log

src/textual/_callback.py

@@ -58,6 +58,7 @@ async def invoke(callback: Callable, *params: object) -> Any:
         # In debug mode we will warn about callbacks that may be stuck
         def log_slow() -> None:
             """Log a message regarding a slow callback."""
+            assert app is not None
             app.log.warning(
                 f"Callback {callback} is still pending after {INVOKE_TIMEOUT_WARNING} seconds"
             )

src/textual/_compositor.py

@@ -14,7 +14,7 @@ without having to render the entire screen.
 from __future__ import annotations
 
 from operator import itemgetter
-from typing import TYPE_CHECKING, Iterable, NamedTuple, cast
+from typing import TYPE_CHECKING, Callable, Iterable, NamedTuple, cast
 
 import rich.repr
 from rich.console import Console, ConsoleOptions, RenderableType, RenderResult
@@ -45,12 +45,23 @@ class ReflowResult(NamedTuple):
 class MapGeometry(NamedTuple):
     """Defines the absolute location of a Widget."""
 
-    region: Region  # The (screen) region occupied by the widget
+    region: Region
-    order: tuple[tuple[int, ...], ...]  # A tuple of ints defining the painting order
+    """The (screen) region occupied by the widget."""
-    clip: Region  # A region to clip the widget by (if a Widget is within a container)
+    order: tuple[tuple[int, int, int], ...]
-    virtual_size: Size  # The virtual size  (scrollable region) of a widget if it is a container
+    """Tuple of tuples defining the painting order of the widget.
-    container_size: Size  # The container size (area not occupied by scrollbars)
+
-    virtual_region: Region  # The region relative to the container (but not necessarily visible)
+    Each successive triple represents painting order information with regards to
+    ancestors in the DOM hierarchy and the last triple provides painting order
+    information for this specific widget.
+    """
+    clip: Region
+    """A region to clip the widget by (if a Widget is within a container)."""
+    virtual_size: Size
+    """The virtual size (scrollable region) of a widget if it is a container."""
+    container_size: Size
+    """The container size (area not occupied by scrollbars)."""
+    virtual_region: Region
+    """The region relative to the container (but not necessarily visible)."""
 
     @property
     def visible_region(self) -> Region:
@@ -419,19 +430,23 @@ class Compositor:
             widget: Widget,
             virtual_region: Region,
             region: Region,
-            order: tuple[tuple[int, ...], ...],
+            order: tuple[tuple[int, int, int], ...],
             layer_order: int,
             clip: Region,
             visible: bool,
-            _MapGeometry=MapGeometry,
+            _MapGeometry: type[MapGeometry] = MapGeometry,
         ) -> None:
             """Called recursively to place a widget and its children in the map.
 
             Args:
                 widget: The widget to add.
+                virtual_region: The Widget region relative to it's container.
                 region: The region the widget will occupy.
-                order: A tuple of ints to define the order.
+                order: Painting order information.
+                layer_order: The order of the widget in its layer.
                 clip: The clipping region (i.e. the viewport which contains it).
+                visible: Whether the widget should be visible by default.
+                    This may be overriden by the CSS rule `visibility`.
             """
             visibility = widget.styles.get_rule("visibility")
             if visibility is not None:
@@ -501,11 +516,12 @@ class Compositor:
                             )
                             widget_region = sub_region + placement_scroll_offset
 
-                        widget_order = (
+                        widget_order = order + (
-                            *order,
+                            (
                                 get_layer_index(sub_widget.layer, 0),
                                 z,
                                 layer_order,
+                            ),
                         )
 
                         add_widget(
@@ -560,7 +576,7 @@ class Compositor:
             root,
             size.region,
             size.region,
-            ((0,),),
+            ((0, 0, 0),),
             layer_order,
             size.region,
             True,
@@ -818,11 +834,8 @@ class Compositor:
         # Maps each cut on to a list of segments
         cuts = self.cuts
 
-        # dict.fromkeys is a callable which takes a list of ints returns a dict which maps ints on to a list of Segments or None.
+        # dict.fromkeys is a callable which takes a list of ints returns a dict which maps ints onto a Segment or None.
-        fromkeys = cast(
+        fromkeys = cast("Callable[[list[int]], dict[int, Strip | None]]", dict.fromkeys)
-            "Callable[[list[int]], dict[int, list[Segment] | None]]", dict.fromkeys
-        )
-        # A mapping of cut index to a list of segments for each line
         chops: list[dict[int, Strip | None]]
         chops = [fromkeys(cut_set[:-1]) for cut_set in cuts]
 

src/textual/_doc.py

@@ -4,7 +4,7 @@ import hashlib
 import os
 import shlex
 from pathlib import Path
-from typing import Iterable
+from typing import Iterable, cast
 
 from textual._import_app import import_app
 from textual.app import App
@@ -45,6 +45,7 @@ def format_svg(source, language, css_class, options, md, attrs, **kwargs) -> str
         import traceback
 
         traceback.print_exception(error)
+        return ""
 
 
 def take_svg_screenshot(
@@ -82,6 +83,7 @@ def take_svg_screenshot(
         hash = hashlib.md5()
         file_paths = [app_path] + app.css_path
         for path in file_paths:
+            assert path is not None
             with open(path, "rb") as source_file:
                 hash.update(source_file.read())
         hash.update(f"{press}-{title}-{terminal_size}".encode("utf-8"))
@@ -105,10 +107,13 @@ def take_svg_screenshot(
 
         app.exit(svg)
 
-    svg = app.run(
+    svg = cast(
+        str,
+        app.run(
             headless=True,
             auto_pilot=auto_pilot,
             size=terminal_size,
+        ),
     )
 
     if app_path is not None:

src/textual/_styles_cache.py

@@ -18,7 +18,7 @@ from .renderables.tint import Tint
 from .strip import Strip
 
 if TYPE_CHECKING:
-    from typing import TypeAlias
+    from typing_extensions import TypeAlias
 
     from .css.styles import StylesBase
     from .widget import Widget

src/textual/_xterm_parser.py

@@ -200,8 +200,8 @@ class XTermParser(Parser[events.Event]):
                     if not bracketed_paste:
                         # Was it a pressed key event that we received?
                         key_events = list(sequence_to_key_events(sequence))
-                        for event in key_events:
+                        for key_event in key_events:
-                            on_token(event)
+                            on_token(key_event)
                         if key_events:
                             break
                         # Or a mouse event?

src/textual/actions.py

@@ -3,6 +3,11 @@ from __future__ import annotations
 import ast
 import re
 
+from typing_extensions import Any, TypeAlias
+
+ActionParseResult: TypeAlias = "tuple[str, tuple[Any, ...]]"
+"""An action is its name and the arbitrary tuple of its parameters."""
+
 
 class SkipAction(Exception):
     """Raise in an action to skip the action (and allow any parent bindings to run)."""
@@ -15,7 +20,7 @@ class ActionError(Exception):
 re_action_params = re.compile(r"([\w\.]+)(\(.*?\))")
 
 
-def parse(action: str) -> tuple[str, tuple[object, ...]]:
+def parse(action: str) -> ActionParseResult:
     """Parses an action string.
 
     Args:

src/textual/app.py

@@ -57,7 +57,7 @@ from ._context import active_app
 from ._event_broker import NoHandler, extract_handler_actions
 from ._path import _make_path_object_relative
 from ._wait import wait_for_idle
-from .actions import SkipAction
+from .actions import ActionParseResult, SkipAction
 from .await_remove import AwaitRemove
 from .binding import Binding, Bindings
 from .css.query import NoMatches
@@ -645,7 +645,7 @@ class App(Generic[ReturnType], DOMNode):
         self,
         group: LogGroup,
         verbosity: LogVerbosity,
-        _textual_calling_frame: inspect.FrameInfo,
+        _textual_calling_frame: inspect.Traceback,
         *objects: Any,
         **kwargs,
     ) -> None:
@@ -1605,9 +1605,8 @@ class App(Generic[ReturnType], DOMNode):
                                 with redirect_stdout(redirector):  # type: ignore
                                     await run_process_messages()
                         else:
-                            null_file = _NullFile()
+                            with redirect_stderr(None):
-                            with redirect_stderr(null_file):
+                                with redirect_stdout(None):
-                                with redirect_stdout(null_file):
                                     await run_process_messages()
 
                 finally:
@@ -1732,16 +1731,17 @@ class App(Generic[ReturnType], DOMNode):
         if not widgets:
             return []
 
-        new_widgets = list(widgets)
+        widget_list: Iterable[Widget]
-
         if before is not None or after is not None:
             # There's a before or after, which means there's going to be an
             # insertion, so make it easier to get the new things in the
             # correct order.
-            new_widgets = reversed(new_widgets)
+            widget_list = reversed(widgets)
+        else:
+            widget_list = widgets
 
         apply_stylesheet = self.stylesheet.apply
-        for widget in new_widgets:
+        for widget in widget_list:
             if not isinstance(widget, Widget):
                 raise AppError(f"Can't register {widget!r}; expected a Widget instance")
             if widget not in self._registry:
@@ -1798,14 +1798,14 @@ class App(Generic[ReturnType], DOMNode):
     async def _close_all(self) -> None:
         """Close all message pumps."""
 
-        # Close all screens on the stack
+        # Close all screens on the stack.
-        for screen in reversed(self._screen_stack):
+        for stack_screen in reversed(self._screen_stack):
-            if screen._running:
+            if stack_screen._running:
-                await self._prune_node(screen)
+                await self._prune_node(stack_screen)
 
         self._screen_stack.clear()
 
-        # Close pre-defined screens
+        # Close pre-defined screens.
         for screen in self.SCREENS.values():
             if isinstance(screen, Screen) and screen._running:
                 await self._prune_node(screen)
@@ -1971,7 +1971,7 @@ class App(Generic[ReturnType], DOMNode):
 
     async def action(
         self,
-        action: str | tuple[str, tuple[str, ...]],
+        action: str | ActionParseResult,
         default_namespace: object | None = None,
     ) -> bool:
         """Perform an action.
@@ -2069,7 +2069,7 @@ class App(Generic[ReturnType], DOMNode):
         else:
             event.stop()
         if isinstance(action, (str, tuple)):
-            await self.action(action, default_namespace=default_namespace)
+            await self.action(action, default_namespace=default_namespace)  # type: ignore[arg-type]
         elif callable(action):
             await action()
         else:
@@ -2339,9 +2339,12 @@ _uvloop_init_done: bool = False
 
 
 def _init_uvloop() -> None:
-    """
+    """Import and install the `uvloop` asyncio policy, if available.
-    Import and install the `uvloop` asyncio policy, if available.
+
     This is done only once, even if the function is called multiple times.
+
+    This is provided as a nicety for users that have `uvloop` installed independently
+    of Textual, as `uvloop` is not listed as a Textual dependency.
     """
     global _uvloop_init_done
 
@@ -2349,10 +2352,10 @@ def _init_uvloop() -> None:
         return
 
     try:
-        import uvloop
+        import uvloop  # type: ignore[reportMissingImports]
     except ImportError:
         pass
     else:
-        uvloop.install()
+        uvloop.install()  # type: ignore[reportUnknownMemberType]
 
     _uvloop_init_done = True

src/textual/cli/previews/easing.py

@@ -92,6 +92,7 @@ class EasingApp(App):
         target_position = (
             END_POSITION if self.position == START_POSITION else START_POSITION
         )
+        assert event.button.id is not None  # Should be set to an easing function str.
         self.animate(
             "position",
             value=target_position,
@@ -106,7 +107,7 @@ class EasingApp(App):
         self.opacity_widget.styles.opacity = 1 - value / END_POSITION
 
     def on_input_changed(self, event: Input.Changed):
-        if event.sender.id == "duration-input":
+        if event.input.id == "duration-input":
             new_duration = _try_float(event.value)
             if new_duration is not None:
                 self.duration = new_duration

src/textual/css/_style_properties.py

@@ -528,8 +528,8 @@ class SpacingProperty:
                 string (e.g. ``"blue on #f0f0f0"``).
 
         Raises:
-            ValueError: When the value is malformed, e.g. a ``tuple`` with a length that is
+            ValueError: When the value is malformed,
-                not 1, 2, or 4.
+                e.g. a ``tuple`` with a length that is not 1, 2, or 4.
         """
         _rich_traceback_omit = True
         if spacing is None:
@@ -543,7 +543,9 @@ class SpacingProperty:
                     str(error),
                     help_text=spacing_wrong_number_of_values_help_text(
                         property_name=self.name,
-                        num_values_supplied=len(spacing),
+                        num_values_supplied=(
+                            1 if isinstance(spacing, int) else len(spacing)
+                        ),
                         context="inline",
                     ),
                 )

src/textual/css/parse.py

@@ -264,7 +264,7 @@ def substitute_references(
 
     iter_tokens = iter(tokens)
 
-    while tokens:
+    while True:
         token = next(iter_tokens, None)
         if token is None:
             break
@@ -274,8 +274,7 @@ def substitute_references(
 
             while True:
                 token = next(iter_tokens, None)
-                # TODO: Mypy error looks legit
+                if token is not None and token.name == "whitespace":
-                if token.name == "whitespace":
                     yield token
                 else:
                     break

src/textual/css/scalar_animation.py

@@ -7,14 +7,14 @@ from .._types import CallbackType
 from .scalar import Scalar, ScalarOffset
 
 if TYPE_CHECKING:
-    from ..dom import DOMNode
+    from ..widget import Widget
     from .styles import StylesBase
 
 
 class ScalarAnimation(Animation):
     def __init__(
         self,
-        widget: DOMNode,
+        widget: Widget,
         styles: StylesBase,
         start_time: float,
         attribute: str,

src/textual/css/styles.py

@@ -335,6 +335,9 @@ class StylesBase(ABC):
             if not isinstance(value, (Scalar, ScalarOffset)):
                 return None
 
+            from ..widget import Widget
+
+            assert isinstance(self.node, Widget)
             return ScalarAnimation(
                 self.node,
                 self,
@@ -581,7 +584,9 @@ class StylesBase(ABC):
 @dataclass
 class Styles(StylesBase):
     node: DOMNode | None = None
-    _rules: RulesMap = field(default_factory=dict)
+    _rules: RulesMap = field(
+        default_factory=lambda: RulesMap()
+    )  # mypy won't be happy with `default_factory=RulesMap`
     _updates: int = 0
 
     important: set[str] = field(default_factory=set)
@@ -648,14 +653,14 @@ class Styles(StylesBase):
         self._updates += 1
         self._rules.clear()  # type: ignore
 
-    def merge(self, other: Styles) -> None:
+    def merge(self, other: StylesBase) -> None:
         """Merge values from another Styles.
 
         Args:
             other: A Styles object.
         """
         self._updates += 1
-        self._rules.update(other._rules)
+        self._rules.update(other.get_rules())
 
     def merge_rules(self, rules: RulesMap) -> None:
         self._updates += 1
@@ -1066,7 +1071,7 @@ class RenderStyles(StylesBase):
     def refresh(self, *, layout: bool = False, children: bool = False) -> None:
         self._inline_styles.refresh(layout=layout, children=children)
 
-    def merge(self, other: Styles) -> None:
+    def merge(self, other: StylesBase) -> None:
         """Merge values from another Styles.
 
         Args:

src/textual/css/stylesheet.py

@@ -78,7 +78,7 @@ class StylesheetErrors:
                     f"{path.absolute() if path else filename}:{line_no}:{col_no}"
                 )
                 link_style = Style(
-                    link=f"file://{path.absolute()}",
+                    link=f"file://{path.absolute()}" if path else None,
                     color="red",
                     bold=True,
                     italic=True,

src/textual/demo.css

@@ -1,4 +1,4 @@
- *  {
+* {
     transition: background 500ms in_out_cubic, color 500ms in_out_cubic;
 }
 
@@ -125,7 +125,7 @@ DarkSwitch Switch {
 }
 
 
-Screen > Container {
+Screen>Container {
     height: 100%;
     overflow: hidden;
 }
@@ -222,7 +222,7 @@ LoginForm {
     border: wide $background;
 }
 
-LoginForm Button{
+LoginForm Button {
     margin: 0 1;
     width: 100%;
 }
@@ -250,7 +250,7 @@ Window {
     max-height: 16;
 }
 
-Window > Static {
+Window>Static {
     width: auto;
 }
 

src/textual/demo.py

@@ -205,7 +205,7 @@ class DarkSwitch(Horizontal):
     def on_mount(self) -> None:
         self.watch(self.app, "dark", self.on_dark_change, init=False)
 
-    def on_dark_change(self, dark: bool) -> None:
+    def on_dark_change(self) -> None:
         self.query_one(Switch).value = self.app.dark
 
     def on_switch_changed(self, event: Switch.Changed) -> None:
@@ -302,7 +302,7 @@ class Notification(Static):
         self.remove()
 
 
-class DemoApp(App):
+class DemoApp(App[None]):
     CSS_PATH = "demo.css"
     TITLE = "Textual Demo"
     BINDINGS = [

src/textual/devtools/client.py

@@ -35,7 +35,7 @@ class DevtoolsLog(NamedTuple):
     """
 
     objects_or_string: tuple[Any, ...] | str
-    caller: inspect.FrameInfo
+    caller: inspect.Traceback
 
 
 class DevtoolsConsole(Console):

src/textual/devtools/redirect_output.py

@@ -39,7 +39,10 @@ class StdoutRedirector:
         if not self.devtools.is_connected:
             return
 
-        previous_frame = inspect.currentframe().f_back
+        current_frame = inspect.currentframe()
+        assert current_frame is not None
+        previous_frame = current_frame.f_back
+        assert previous_frame is not None
         caller = inspect.getframeinfo(previous_frame)
 
         self._buffer.append(DevtoolsLog(string, caller=caller))

src/textual/devtools/service.py

@@ -5,10 +5,10 @@ import asyncio
 import json
 import pickle
 from json import JSONDecodeError
-from typing import Any, cast
+from typing import Any
 
 import msgpack
-from aiohttp import WSMessage, WSMsgType
+from aiohttp import WSMsgType
 from aiohttp.abc import Request
 from aiohttp.web_ws import WebSocketResponse
 from rich.console import Console

src/textual/dom.py

@@ -24,7 +24,7 @@ from rich.tree import Tree
 from ._context import NoActiveAppError
 from ._node_list import NodeList
 from ._types import CallbackType
-from .binding import Bindings, BindingType
+from .binding import Binding, Bindings, BindingType
 from .color import BLACK, WHITE, Color
 from .css._error_tools import friendly_list
 from .css.constants import VALID_DISPLAY, VALID_VISIBILITY
@@ -39,7 +39,7 @@ from .walk import walk_breadth_first, walk_depth_first
 
 if TYPE_CHECKING:
     from .app import App
-    from .css.query import DOMQuery
+    from .css.query import DOMQuery, QueryType
     from .screen import Screen
     from .widget import Widget
     from typing_extensions import TypeAlias
@@ -276,7 +276,7 @@ class DOMNode(MessagePump):
                         base.__dict__.get("BINDINGS", []),
                     )
                 )
-        keys = {}
+        keys: dict[str, Binding] = {}
         for bindings_ in bindings:
             keys.update(bindings_.keys)
         return Bindings(keys.values())
@@ -357,7 +357,7 @@ class DOMNode(MessagePump):
         # Note that self.screen may not be the same as self.app.screen
         from .screen import Screen
 
-        node = self
+        node: MessagePump | None = self
         while node is not None and not isinstance(node, Screen):
             node = node._parent
         if not isinstance(node, Screen):
@@ -771,19 +771,17 @@ class DOMNode(MessagePump):
             nodes.reverse()
         return cast("list[DOMNode]", nodes)
 
-    ExpectType = TypeVar("ExpectType", bound="Widget")
-
     @overload
     def query(self, selector: str | None) -> DOMQuery[Widget]:
         ...
 
     @overload
-    def query(self, selector: type[ExpectType]) -> DOMQuery[ExpectType]:
+    def query(self, selector: type[QueryType]) -> DOMQuery[QueryType]:
         ...
 
     def query(
-        self, selector: str | type[ExpectType] | None = None
+        self, selector: str | type[QueryType] | None = None
-    ) -> DOMQuery[Widget] | DOMQuery[ExpectType]:
+    ) -> DOMQuery[Widget] | DOMQuery[QueryType]:
         """Get a DOM query matching a selector.
 
         Args:
@@ -792,33 +790,31 @@ class DOMNode(MessagePump):
         Returns:
             A query object.
         """
-        from .css.query import DOMQuery
+        from .css.query import DOMQuery, QueryType
+        from .widget import Widget
 
-        query: str | None
         if isinstance(selector, str) or selector is None:
-            query = selector
+            return DOMQuery[Widget](self, filter=selector)
         else:
-            query = selector.__name__
+            return DOMQuery[QueryType](self, filter=selector.__name__)
-
-        return DOMQuery(self, filter=query)
 
     @overload
     def query_one(self, selector: str) -> Widget:
         ...
 
     @overload
-    def query_one(self, selector: type[ExpectType]) -> ExpectType:
+    def query_one(self, selector: type[QueryType]) -> QueryType:
         ...
 
     @overload
-    def query_one(self, selector: str, expect_type: type[ExpectType]) -> ExpectType:
+    def query_one(self, selector: str, expect_type: type[QueryType]) -> QueryType:
         ...
 
     def query_one(
         self,
-        selector: str | type[ExpectType],
+        selector: str | type[QueryType],
-        expect_type: type[ExpectType] | None = None,
+        expect_type: type[QueryType] | None = None,
-    ) -> ExpectType | Widget:
+    ) -> QueryType | Widget:
         """Get a single Widget matching the given selector or selector type.
 
         Args:

src/textual/events.py

@@ -5,7 +5,7 @@ from typing import TYPE_CHECKING, Awaitable, Callable, Type, TypeVar
 import rich.repr
 from rich.style import Style
 
-from ._types import MessageTarget
+from ._types import CallbackType, MessageTarget
 from .geometry import Offset, Size
 from .keys import _get_key_aliases
 from .message import Message
@@ -28,11 +28,7 @@ class Event(Message):
 
 @rich.repr.auto
 class Callback(Event, bubble=False, verbose=True):
-    def __init__(
+    def __init__(self, sender: MessageTarget, callback: CallbackType) -> None:
-        self,
-        sender: MessageTarget,
-        callback: Callable[[], Awaitable[None]],
-    ) -> None:
         self.callback = callback
         super().__init__(sender)
 

src/textual/keys.py

@@ -5,7 +5,7 @@ from enum import Enum
 
 
 # Adapted from prompt toolkit https://github.com/prompt-toolkit/python-prompt-toolkit/blob/master/prompt_toolkit/keys.py
-class Keys(str, Enum):
+class Keys(str, Enum):  # type: ignore[no-redef]
     """
     List of keys for use in key bindings.
 
@@ -13,7 +13,9 @@ class Keys(str, Enum):
     strings.
     """
 
-    value: str
+    @property
+    def value(self) -> str:
+        return super().value
 
     Escape = "escape"  # Also Control-[
     ShiftEscape = "shift+escape"

src/textual/screen.py

@@ -12,7 +12,7 @@ from ._compositor import Compositor, MapGeometry
 from ._types import CallbackType
 from .css.match import match
 from .css.parse import parse_selectors
-from .dom import DOMNode
+from .css.query import QueryType
 from .geometry import Offset, Region, Size
 from .reactive import Reactive
 from .renderables.blank import Blank
@@ -169,7 +169,7 @@ class Screen(Widget):
         return widgets
 
     def _move_focus(
-        self, direction: int = 0, selector: str | type[DOMNode.ExpectType] = "*"
+        self, direction: int = 0, selector: str | type[QueryType] = "*"
     ) -> Widget | None:
         """Move the focus in the given direction.
 
@@ -230,9 +230,7 @@ class Screen(Widget):
 
         return self.focused
 
-    def focus_next(
+    def focus_next(self, selector: str | type[QueryType] = "*") -> Widget | None:
-        self, selector: str | type[DOMNode.ExpectType] = "*"
-    ) -> Widget | None:
         """Focus the next widget, optionally filtered by a CSS selector.
 
         If no widget is currently focused, this will focus the first focusable widget.
@@ -249,9 +247,7 @@ class Screen(Widget):
         """
         return self._move_focus(1, selector)
 
-    def focus_previous(
+    def focus_previous(self, selector: str | type[QueryType] = "*") -> Widget | None:
-        self, selector: str | type[DOMNode.ExpectType] = "*"
-    ) -> Widget | None:
         """Focus the previous widget, optionally filtered by a CSS selector.
 
         If no widget is currently focused, this will focus the first focusable widget.

src/textual/scrollbar.py

@@ -300,13 +300,13 @@ class ScrollBar(Widget):
     def _on_leave(self, event: events.Leave) -> None:
         self.mouse_over = False
 
-    async def action_scroll_down(self) -> None:
+    def action_scroll_down(self) -> None:
-        await self.post_message(
+        self.post_message_no_wait(
             ScrollDown(self) if self.vertical else ScrollRight(self)
         )
 
-    async def action_scroll_up(self) -> None:
+    def action_scroll_up(self) -> None:
-        await self.post_message(ScrollUp(self) if self.vertical else ScrollLeft(self))
+        self.post_message_no_wait(ScrollUp(self) if self.vertical else ScrollLeft(self))
 
     def action_grab(self) -> None:
         self.capture_mouse()

src/textual/widget.py

@@ -65,6 +65,7 @@ from .walk import walk_depth_first
 
 if TYPE_CHECKING:
     from .app import App, ComposeResult
+    from .message_pump import MessagePump
     from .scrollbar import (
         ScrollBar,
         ScrollBarCorner,
@@ -443,22 +444,26 @@ class Widget(DOMNode):
         self, id: str, expect_type: type[ExpectType] | None = None
     ) -> ExpectType | Widget:
         """Return the first descendant widget with the given ID.
+
         Performs a depth-first search rooted at this widget.
 
         Args:
-            id: The ID to search for in the subtree
+            id: The ID to search for in the subtree.
             expect_type: Require the object be of the supplied type, or None for any type.
-                Defaults to None.
 
         Returns:
             The first descendant encountered with this ID.
 
         Raises:
-            NoMatches: if no children could be found for this ID
+            NoMatches: if no children could be found for this ID.
             WrongType: if the wrong type was found.
         """
-        for child in walk_depth_first(self):
+        # We use Widget as a filter_type so that the inferred type of child is Widget.
+        for child in walk_depth_first(self, filter_type=Widget):
             try:
+                if expect_type is None:
+                    return child.get_child_by_id(id)
+                else:
                     return child.get_child_by_id(id, expect_type=expect_type)
             except NoMatches:
                 pass
@@ -729,7 +734,9 @@ class Widget(DOMNode):
 
         # Ensure the child and target are widgets.
         child = _to_widget(child, "move")
-        target = _to_widget(before if after is None else after, "move towards")
+        target = _to_widget(
+            cast("int | Widget", before if after is None else after), "move towards"
+        )
 
         # At this point we should know what we're moving, and it should be a
         # child; where we're moving it to, which should be within the child
@@ -2275,7 +2282,7 @@ class Widget(DOMNode):
             Names of the pseudo classes.
 
         """
-        node = self
+        node: MessagePump | None = self
         while isinstance(node, Widget):
             if node.disabled:
                 yield "disabled"
@@ -2322,7 +2329,9 @@ class Widget(DOMNode):
             renderable.justify = text_justify
 
         renderable = _Styled(
-            renderable, self.rich_style, self.link_style if self.auto_links else None
+            cast(ConsoleRenderable, renderable),
+            self.rich_style,
+            self.link_style if self.auto_links else None,
         )
 
         return renderable
@@ -2524,7 +2533,7 @@ class Widget(DOMNode):
         self.check_idle()
 
     def remove(self) -> AwaitRemove:
-        """Remove the Widget from the DOM (effectively deleting it)
+        """Remove the Widget from the DOM (effectively deleting it).
 
         Returns:
             An awaitable object that waits for the widget to be removed.
@@ -2537,16 +2546,16 @@ class Widget(DOMNode):
         """Get renderable for widget.
 
         Returns:
-            Any renderable
+            Any renderable.
         """
-        render = "" if self.is_container else self.css_identifier_styled
+        render: Text | str = "" if self.is_container else self.css_identifier_styled
         return render
 
     def _render(self) -> ConsoleRenderable | RichCast:
         """Get renderable, promoting str to text as required.
 
         Returns:
-            A renderable
+            A renderable.
         """
         renderable = self.render()
         if isinstance(renderable, str):

src/textual/widgets/_button.py

@@ -4,7 +4,6 @@ from functools import partial
 from typing import cast
 
 import rich.repr
-from rich.console import RenderableType
 from rich.text import Text, TextType
 from typing_extensions import Literal
 
@@ -145,7 +144,7 @@ class Button(Static, can_focus=True):
     ACTIVE_EFFECT_DURATION = 0.3
     """When buttons are clicked they get the `-active` class for this duration (in seconds)"""
 
-    label: reactive[RenderableType] = reactive[RenderableType]("")
+    label: reactive[TextType] = reactive[TextType]("")
     """The text label that appears within the button."""
 
     variant = reactive("default")
@@ -209,15 +208,14 @@ class Button(Static, can_focus=True):
         self.remove_class(f"-{old_variant}")
         self.add_class(f"-{variant}")
 
-    def validate_label(self, label: RenderableType) -> RenderableType:
+    def validate_label(self, label: TextType) -> TextType:
         """Parse markup for self.label"""
         if isinstance(label, str):
             return Text.from_markup(label)
         return label
 
-    def render(self) -> RenderableType:
+    def render(self) -> TextType:
-        label = self.label.copy()
+        label = Text.assemble(" ", self.label, " ")
-        label = Text.assemble(" ", label, " ")
         label.stylize(self.text_style)
         return label
 

src/textual/widgets/_footer.py

@@ -66,7 +66,7 @@ class Footer(Widget):
         self.refresh()
 
     def on_mount(self) -> None:
-        self.watch(self.screen, "focused", self._focus_changed)
+        self.watch(self.screen, "focused", self._focus_changed)  # type: ignore[arg-type]
 
     def _focus_changed(self, focused: Widget | None) -> None:
         self._key_text = None

src/textual/widgets/_header.py

@@ -133,5 +133,5 @@ class Header(Widget):
         def set_sub_title(sub_title: str) -> None:
             self.query_one(HeaderTitle).sub_text = sub_title
 
-        self.watch(self.app, "title", set_title)
+        self.watch(self.app, "title", set_title)  # type: ignore[arg-type]
-        self.watch(self.app, "sub_title", set_sub_title)
+        self.watch(self.app, "sub_title", set_sub_title)  # type: ignore[arg-type]

src/textual/widgets/_list_item.py

@@ -31,7 +31,7 @@ class ListItem(Widget, can_focus=False):
     class _ChildClicked(Message):
         """For informing with the parent ListView that we were clicked"""
 
-        pass
+        sender: "ListItem"
 
     def on_click(self, event: events.Click) -> None:
         self.post_message_no_wait(self._ChildClicked(self))

src/textual/widgets/_list_view.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import ClassVar
+from typing import ClassVar, Optional
 
 from textual.await_remove import AwaitRemove
 from textual.binding import Binding, BindingType
@@ -8,7 +8,7 @@ from textual.containers import Vertical
 from textual.geometry import clamp
 from textual.message import Message
 from textual.reactive import reactive
-from textual.widget import AwaitMount
+from textual.widget import AwaitMount, Widget
 from textual.widgets._list_item import ListItem
 
 
@@ -35,7 +35,7 @@ class ListView(Vertical, can_focus=True, can_focus_children=False):
     | down | Move the cursor down. |
     """
 
-    index = reactive(0, always_update=True)
+    index = reactive[Optional[int]](0, always_update=True)
 
     class Highlighted(Message, bubble=True):
         """Posted when the highlighted item changes.
@@ -96,10 +96,12 @@ class ListView(Vertical, can_focus=True, can_focus_children=False):
     @property
     def highlighted_child(self) -> ListItem | None:
         """The currently highlighted ListItem, or None if nothing is highlighted."""
-        if self.index is None:
+        if self.index is not None and 0 <= self.index < len(self._nodes):
+            list_item = self._nodes[self.index]
+            assert isinstance(list_item, ListItem)
+            return list_item
+        else:
             return None
-        elif 0 <= self.index < len(self._nodes):
-            return self._nodes[self.index]
 
     def validate_index(self, index: int | None) -> int | None:
         """Clamp the index to the valid range, or set to None if there's nothing to highlight.
@@ -129,9 +131,13 @@ class ListView(Vertical, can_focus=True, can_focus_children=False):
         """Updates the highlighting when the index changes."""
         if self._is_valid_index(old_index):
             old_child = self._nodes[old_index]
+            assert isinstance(old_child, ListItem)
             old_child.highlighted = False
+
+        new_child: Widget | None
         if self._is_valid_index(new_index):
             new_child = self._nodes[new_index]
+            assert isinstance(new_child, ListItem)
             new_child.highlighted = True
         else:
             new_child = None
@@ -168,14 +174,22 @@ class ListView(Vertical, can_focus=True, can_focus_children=False):
     def action_select_cursor(self) -> None:
         """Select the current item in the list."""
         selected_child = self.highlighted_child
+        if selected_child is None:
+            return
         self.post_message_no_wait(self.Selected(self, selected_child))
 
     def action_cursor_down(self) -> None:
         """Highlight the next item in the list."""
+        if self.index is None:
+            self.index = 0
+            return
         self.index += 1
 
     def action_cursor_up(self) -> None:
         """Highlight the previous item in the list."""
+        if self.index is None:
+            self.index = 0
+            return
         self.index -= 1
 
     def on_list_item__child_clicked(self, event: ListItem._ChildClicked) -> None: