App

Here you will find the App class, which is the base class for Textual apps.

See app basics for how to build Textual apps.

AutopilotCallbackType module-attribute

AutopilotCallbackType: TypeAlias = (
    "Callable[[Pilot[object]], Coroutine[Any, Any, None]]"
)

Signature for valid callbacks that can be used to control apps.

CSSPathType module-attribute

CSSPathType = Union[
    str, PurePath, List[Union[str, PurePath]]
]

Valid ways of specifying paths to CSS files.

ActionError class

Bases: Exception

Base class for exceptions relating to actions.

ActiveModeError class

Bases: ModeError

Raised when attempting to remove the currently active mode.

App class

def __init__(
    self, driver_class=None, css_path=None, watch_css=False
):

Bases: Generic[ReturnType], DOMNode

The base class for Textual Applications.

Parameters

Name	Type	Description	Default
driver_class	Type[Driver] | None	Driver class or None to auto-detect. This will be used by some Textual tools.	None
css_path	CSSPathType | None	Path to CSS or None to use the CSS_PATH class variable. To load multiple CSS files, pass a list of strings or paths which will be loaded in order.	None
watch_css	bool	Reload CSS if the files changed. This is set automatically if you are using textual run with the dev switch.	False

Raises

Type	Description
CssPathError	When the supplied CSS path(s) are an unexpected type.

AUTO_FOCUS class-attribute

AUTO_FOCUS: str | None = '*'

A selector to determine what to focus automatically when a screen is activated.

The widget focused is the first that matches the given CSS selector. Setting to None or "" disables auto focus.

COMMANDS class-attribute

COMMANDS: set[type[Provider]] = {SystemCommands}

Command providers used by the command palette.

Should be a set of command.Provider classes.

CSS class-attribute

CSS: str = ''

Inline CSS, useful for quick scripts. This is loaded after CSS_PATH, and therefore takes priority in the event of a specificity clash.

CSS_PATH class-attribute

CSS_PATH: CSSPathType | None = None

File paths to load CSS from.

ENABLE_COMMAND_PALETTE class-attribute

ENABLE_COMMAND_PALETTE: bool = True

Should the command palette be enabled for the application?

MODES class-attribute

MODES: dict[str, str | Screen | Callable[[], Screen]] = {}

Modes associated with the app and their base screens.

The base screen is the screen at the bottom of the mode stack. You can think of it as the default screen for that stack. The base screens can be names of screens listed in SCREENS, Screen instances, or callables that return screens.

Example

class HelpScreen(Screen[None]):
    ...

class MainAppScreen(Screen[None]):
    ...

class MyApp(App[None]):
    MODES = {
        "default": "main",
        "help": HelpScreen,
    }

    SCREENS = {
        "main": MainAppScreen,
    }

    ...

SCREENS class-attribute

SCREENS: dict[str, Screen | Callable[[], Screen]] = {}

Screens associated with the app for the lifetime of the app.

SUB_TITLE class-attribute instance-attribute

SUB_TITLE: str | None = None

A class variable to set the default sub-title for the application.

To update the sub-title while the app is running, you can set the sub_title attribute. See also the Screen.SUB_TITLE attribute.

TITLE class-attribute instance-attribute

TITLE: str | None = None

A class variable to set the default title for the application.

To update the title while the app is running, you can set the title attribute. See also the Screen.TITLE attribute.

children property

children: Sequence['Widget']

A view onto the app's immediate children.

This attribute exists on all widgets. In the case of the App, it will only ever contain a single child, which will be the currently active screen.

Returns

Type	Description
Sequence['Widget']	A sequence of widgets.

current_mode property

current_mode: str

The name of the currently active mode.

dark class-attribute instance-attribute

dark: Reactive[bool] = Reactive(True, compute=False)

Use a dark theme if True, otherwise use a light theme.

Modify this attribute to switch between light and dark themes.

Example

self.app.dark = not self.app.dark  # Toggle dark mode

debug property

debug: bool

Is debug mode enabled?

focused property

focused: Widget | None

The widget that is focused on the currently active screen, or None.

Focused widgets receive keyboard input.

Returns

Type	Description
Widget | None	The currently focused widget, or None if nothing is focused.

is_headless property

is_headless: bool

Is the driver running in 'headless' mode?

Headless mode is used when running tests with run_test.

log property

log: Logger

The textual logger.

Example

self.log("Hello, World!")
self.log(self.tree)

Returns

Type	Description
Logger	A Textual logger.

namespace_bindings property

namespace_bindings: dict[str, tuple[DOMNode, Binding]]

Get currently active bindings.

If no widget is focused, then app-level bindings are returned. If a widget is focused, then any bindings present in the active screen and app are merged and returned.

This property may be used to inspect current bindings.

Returns

Type	Description
dict[str, tuple[DOMNode, Binding]]	A mapping of keys onto pairs of nodes and bindings.

return_code property

return_code: int | None

The return code with which the app exited.

Non-zero codes indicate errors. A value of 1 means the app exited with a fatal error. If the app wasn't exited yet, this will be None.

Example

The return code can be used to exit the process via sys.exit.

my_app.run()
sys.exit(my_app.return_code)

return_value property

return_value: ReturnType | None

The return value of the app, or None if it has not yet been set.

The return value is set when calling exit.

screen property

screen: Screen[object]

The current active screen.

Returns

Type	Description
Screen[object]	The currently active (visible) screen.

Raises

Type	Description
ScreenStackError	If there are no screens on the stack.

screen_stack property

screen_stack: Sequence[Screen]

A snapshot of the current screen stack.

Returns

Type	Description
Sequence[Screen]	A snapshot of the current state of the screen stack.

scroll_sensitivity_x instance-attribute

scroll_sensitivity_x: float = 4.0

Number of columns to scroll in the X direction with wheel or trackpad.

scroll_sensitivity_y instance-attribute

scroll_sensitivity_y: float = 2.0

Number of lines to scroll in the Y direction with wheel or trackpad.

size property

size: Size

The size of the terminal.

Returns

Type	Description
Size	Size of the terminal.

sub_title class-attribute instance-attribute

sub_title: Reactive[str] = (
    self.SUB_TITLE if self.SUB_TITLE is not None else ""
)

The sub-title for the application.

The initial value for sub_title will be set to the SUB_TITLE class variable if it exists, or an empty string if it doesn't.

Sub-titles are typically used to show the high-level state of the app, such as the current mode, or path to the file being worked on.

Assign a new value to this attribute to change the sub-title. The new value is always converted to string.

title class-attribute instance-attribute

title: Reactive[str] = (
    self.TITLE
    if self.TITLE is not None
    else f"{self.__class__.__name__}"
)

The title for the application.

The initial value for title will be set to the TITLE class variable if it exists, or the name of the app if it doesn't.

Assign a new value to this attribute to change the title. The new value is always converted to string.

use_command_palette instance-attribute

use_command_palette: bool = self.ENABLE_COMMAND_PALETTE

A flag to say if the application should use the command palette.

If set to False any call to action_command_palette will be ignored.

workers property

workers: WorkerManager

The worker manager.

Returns

Type	Description
WorkerManager	An object to manage workers.

action_add_class async

def action_add_class(self, selector, class_name):

An action to add a CSS class to the selected widget.

Parameters

Name	Type	Description	Default
selector	str	Selects the widget to add the class to.	required
class_name	str	The class to add to the selected widget.	required

action_back async

def action_back(self):

An action to go back to the previous screen (pop the current screen).

Note

If there is no screen to go back to, this is a non-operation (in other words it's safe to call even if there are no other screens on the stack.)

action_bell async

def action_bell(self):

An action to play the terminal 'bell'.

action_check_bindings async

def action_check_bindings(self, key):

An action to handle a key press using the binding system.

Parameters

Name	Type	Description	Default
key	str	The key to process.	required

action_command_palette method

def action_command_palette(self):

Show the Textual command palette.

action_focus async

def action_focus(self, widget_id):

An action to focus the given widget.

Parameters

Name	Type	Description	Default
widget_id	str	ID of widget to focus.	required

action_focus_next method

def action_focus_next(self):

An action to focus the next widget.

action_focus_previous method

def action_focus_previous(self):

An action to focus the previous widget.

action_pop_screen async

def action_pop_screen(self):

An action to remove the topmost screen and makes the new topmost screen active.

action_push_screen async

def action_push_screen(self, screen):

An action to push a new screen on to the stack and make it active.

Parameters

Name	Type	Description	Default
screen	str	Name of the screen.	required

action_quit async

def action_quit(self):

An action to quit the app as soon as possible.

action_remove_class async

def action_remove_class(self, selector, class_name):

An action to remove a CSS class from the selected widget.

Parameters

Name	Type	Description	Default
selector	str	Selects the widget to remove the class from.	required
class_name	str	The class to remove from the selected widget.	required

action_screenshot method

def action_screenshot(self, filename=None, path='./'):

This action will save an SVG file containing the current contents of the screen.

Parameters

Name	Type	Description	Default
filename	str | None	Filename of screenshot, or None to auto-generate.	None
path	str	Path to directory. Defaults to current working directory.	'./'

action_switch_mode async

def action_switch_mode(self, mode):

An action that switches to the given mode..

action_switch_screen async

def action_switch_screen(self, screen):

An action to switch screens.

Parameters

Name	Type	Description	Default
screen	str	Name of the screen.	required

action_toggle_class async

def action_toggle_class(self, selector, class_name):

An action to toggle a CSS class on the selected widget.

Parameters

Name	Type	Description	Default
selector	str	Selects the widget to toggle the class on.	required
class_name	str	The class to toggle on the selected widget.	required

action_toggle_dark method

def action_toggle_dark(self):

An action to toggle dark mode.

add_mode method

def add_mode(self, mode, base_screen):

Adds a mode and its corresponding base screen to the app.

Parameters

Name	Type	Description	Default
mode	str	The new mode.	required
base_screen	str | Screen | Callable[[], Screen]	The base screen associated with the given mode.	required

Raises

Type	Description
InvalidModeError	If the name of the mode is not valid/duplicated.

animate method

def animate(
    self,
    attribute,
    value,
    *,
    final_value=Ellipsis,
    duration=None,
    speed=None,
    delay=0.0,
    easing=DEFAULT_EASING,
    on_complete=None
):

Animate an attribute.

See the guide for how to use the animation system.

Parameters

Name	Type	Description	Default
attribute	str	Name of the attribute to animate.	required
value	float | Animatable	The value to animate to.	required
final_value	object	The final value of the animation.	Ellipsis
duration	float | None	The duration of the animate.	None
speed	float | None	The speed of the animation.	None
delay	float	A delay (in seconds) before the animation starts.	0.0
easing	EasingFunction | str	An easing method.	DEFAULT_EASING
on_complete	CallbackType | None	A callable to invoke when the animation is finished.	None

batch_update method

def batch_update(self):

A context manager to suspend all repaints until the end of the batch.

begin_capture_print method

def begin_capture_print(self, target, stdout=True, stderr=True):

Capture content that is printed (or written to stdout / stderr).

If printing is captured, the target will be send an events.Print message.

Parameters

Name	Type	Description	Default
target	MessageTarget	The widget where print content will be sent.	required
stdout	bool	Capture stdout.	True
stderr	bool	Capture stderr.	True

bell method

def bell(self):

Play the console 'bell'.

For terminals that support a bell, this typically makes a notification or error sound. Some terminals may make no sound or display a visual bell indicator, depending on configuration.

bind method

def bind(
    self,
    keys,
    action,
    *,
    description="",
    show=True,
    key_display=None
):

Bind a key to an action.

Parameters

Name	Type	Description	Default
keys	str	A comma separated list of keys, i.e.	required
action	str	Action to bind to.	required
description	str	Short description of action.	''
show	bool	Show key in UI.	True
key_display	str | None	Replacement text for key, or None to use default.	None

call_from_thread method

def call_from_thread(self, callback, *args, **kwargs):

Run a callable from another thread, and return the result.

Like asyncio apps in general, Textual apps are not thread-safe. If you call methods or set attributes on Textual objects from a thread, you may get unpredictable results.

This method will ensure that your code runs within the correct context.

Tip

Consider using post_message which is also thread-safe.

Parameters

Name	Type	Description	Default
callback	Callable[..., CallThreadReturnType | Awaitable[CallThreadReturnType]]	A callable to run.	required
*args	object	Arguments to the callback.	()
**kwargs	object	Keyword arguments for the callback.	{}

Raises

Type	Description
RuntimeError	If the app isn't running or if this method is called from the same thread where the app is running.

Returns

Type	Description
CallThreadReturnType	The result of the callback.

capture_mouse method

def capture_mouse(self, widget):

Send all mouse events to the given widget or disable mouse capture.

Parameters

Name	Type	Description	Default
widget	Widget | None	If a widget, capture mouse event, or None to end mouse capture.	required

check_bindings async

def check_bindings(self, key, priority=False):

Handle a key press.

This method is used internally by the bindings system, but may be called directly if you wish to simulate a key being pressed.

Parameters

Name	Type	Description	Default
key	str	A key.	required
priority	bool	If True check from App down, otherwise from focused up.	False

Returns

Type	Description
bool	True if the key was handled by a binding, otherwise False

clear_notifications method

def clear_notifications(self):

Clear all the current notifications.

end_capture_print method

def end_capture_print(self, target):

End capturing of prints.

Parameters

Name	Type	Description	Default
target	MessageTarget	The widget that was capturing prints.	required

exit method

def exit(self, result=None, return_code=0, message=None):

Exit the app, and return the supplied result.

Parameters

Name	Type	Description	Default
result	ReturnType | None	Return value.	None
return_code	int	The return code. Use non-zero values for error codes.	0
message	RenderableType | None	Optional message to display on exit.	None

export_screenshot method

def export_screenshot(self, *, title=None):

Export an SVG screenshot of the current screen.

See also save_screenshot which writes the screenshot to a file.

Parameters

Name	Type	Description	Default
title	str | None	The title of the exported screenshot or None to use app title.	None

get_child_by_id method

def get_child_by_id(self, id, expect_type=None):

Get the first child (immediate descendent) of this DOMNode with the given ID.

Parameters

Name	Type	Description	Default
id	str	The ID of the node to search for.	required
expect_type	type[ExpectType] | None	Require the object be of the supplied type, or use None to apply no type restriction.	None

Returns

Type	Description
ExpectType | Widget	The first child of this node with the specified ID.

Raises

Type	Description
NoMatches	If no children could be found for this ID.
WrongType	If the wrong type was found.

get_child_by_type method

def get_child_by_type(self, expect_type):

Get a child of a give type.

Parameters

Name	Type	Description	Default
expect_type	type[ExpectType]	The type of the expected child.	required

Raises

Type	Description
NoMatches	If no valid child is found.

Returns

Type	Description
ExpectType	A widget.

get_css_variables method

def get_css_variables(self):

Get a mapping of variables used to pre-populate CSS.

May be implemented in a subclass to add new CSS variables.

Returns

Type	Description
dict[str, str]	A mapping of variable name to value.

get_driver_class method

def get_driver_class(self):

Get a driver class for this platform.

This method is called by the constructor, and unlikely to be required when building a Textual app.

Returns

Type	Description
Type[Driver]	A Driver class which manages input and display.

get_key_display method

def get_key_display(self, key):

For a given key, return how it should be displayed in an app (e.g. in the Footer widget). By key, we refer to the string used in the "key" argument for a Binding instance. By overriding this method, you can ensure that keys are displayed consistently throughout your app, without needing to add a key_display to every binding.

Parameters

Name	Type	Description	Default
key	str	The binding key string.	required

Returns

Type	Description
str	The display string for the input key.

get_screen method

def get_screen(self, screen):

Get an installed screen.

Parameters

Name	Type	Description	Default
screen	Screen | str	Either a Screen object or screen name (the name argument when installed).	required

Raises

Type	Description
KeyError	If the named screen doesn't exist.

Returns

Type	Description
Screen	A screen instance.

get_widget_at method

def get_widget_at(self, x, y):

Get the widget under the given coordinates.

Parameters

Name	Type	Description	Default
x	int	X coordinate.	required
y	int	Y coordinate.	required

Returns

Type	Description
tuple[Widget, Region]	The widget and the widget's screen region.

get_widget_by_id method

def get_widget_by_id(self, id, expect_type=None):

Get the first descendant widget with the given ID.

Performs a breadth-first search rooted at the current screen. It will not return the Screen if that matches the ID. To get the screen, use self.screen.

Parameters

Name	Type	Description	Default
id	str	The ID to search for in the subtree	required
expect_type	type[ExpectType] | None	Require the object be of the supplied type, or None for any type. Defaults to None.	None

Returns

Type	Description
ExpectType | Widget	The first descendant encountered with this ID.

Raises

Type	Description
NoMatches	if no children could be found for this ID
WrongType	if the wrong type was found.

install_screen method

def install_screen(self, screen, name):

Install a screen.

Installing a screen prevents Textual from destroying it when it is no longer on the screen stack. Note that you don't need to install a screen to use it. See push_screen or switch_screen to make a new screen current.

Parameters

Name	Type	Description	Default
screen	Screen	Screen to install.	required
name	str	Unique name to identify the screen.	required

Raises

Type	Description
ScreenError	If the screen can't be installed.

Returns

Type	Description
None	An awaitable that awaits the mounting of the screen and its children.

is_mounted method

def is_mounted(self, widget):

Check if a widget is mounted.

Parameters

Name	Type	Description	Default
widget	Widget	A widget.	required

Returns

Type	Description
bool	True of the widget is mounted.

is_screen_installed method

def is_screen_installed(self, screen):

Check if a given screen has been installed.

Parameters

Name	Type	Description	Default
screen	Screen | str	Either a Screen object or screen name (the name argument when installed).	required

Returns

Type	Description
bool	True if the screen is currently installed,

mount method

def mount(self, *widgets, before=None, after=None):

Mount the given widgets relative to the app's screen.

Parameters

Name	Type	Description	Default
*widgets	Widget	The widget(s) to mount.	()
before	int | str | Widget | None	Optional location to mount before. An int is the index of the child to mount before, a str is a query_one query to find the widget to mount before.	None
after	int | str | Widget | None	Optional location to mount after. An int is the index of the child to mount after, a str is a query_one query to find the widget to mount after.	None

Returns

Type	Description
AwaitMount	An awaitable object that waits for widgets to be mounted.

Raises

Type	Description
MountError	If there is a problem with the mount request.

Note

Only one of before or after can be provided. If both are provided a MountError will be raised.

mount_all method

def mount_all(self, widgets, *, before=None, after=None):

Mount widgets from an iterable.

Parameters

Name	Type	Description	Default
widgets	Iterable[Widget]	An iterable of widgets.	required
before	int | str | Widget | None	Optional location to mount before. An int is the index of the child to mount before, a str is a query_one query to find the widget to mount before.	None
after	int | str | Widget | None	Optional location to mount after. An int is the index of the child to mount after, a str is a query_one query to find the widget to mount after.	None

Returns

Type	Description
AwaitMount	An awaitable object that waits for widgets to be mounted.

Raises

Type	Description
MountError	If there is a problem with the mount request.

Note

Only one of before or after can be provided. If both are provided a MountError will be raised.

notify method

def notify(
    self,
    message,
    *,
    title="",
    severity="information",
    timeout=Notification.timeout
):

Create a notification.

Tip

This method is thread-safe.

Parameters

Name	Type	Description	Default
message	str	The message for the notification.	required
title	str	The title for the notification.	''
severity	SeverityLevel	The severity of the notification.	'information'
timeout	float	The timeout for the notification.	Notification.timeout

The notify method is used to create an application-wide notification, shown in a Toast, normally originating in the bottom right corner of the display.

Notifications can have the following severity levels:

• information
• warning
• error

The default is information.

Example

# Show an information notification.
self.notify("It's an older code, sir, but it checks out.")

# Show a warning. Note that Textual's notification system allows
# for the use of Rich console markup.
self.notify(
    "Now witness the firepower of this fully "
    "[b]ARMED[/b] and [i][b]OPERATIONAL[/b][/i] battle station!",
    title="Possible trap detected",
    severity="warning",
)

# Show an error. Set a longer timeout so it's noticed.
self.notify("It's a trap!", severity="error", timeout=10)

# Show an information notification, but without any sort of title.
self.notify("It's against my programming to impersonate a deity.", title="")

panic method

def panic(self, *renderables):

Exits the app and display error message(s).

Used in response to unexpected errors. For a more graceful exit, see the exit method.

Parameters

Name	Type	Description	Default
*renderables	RenderableType	Text or Rich renderable(s) to display on exit.	()

pop_screen method

def pop_screen(self):

Pop the current screen from the stack, and switch to the previous screen.

Returns

Type	Description
Screen[object]	The screen that was replaced.

post_display_hook method

def post_display_hook(self):

Called immediately after a display is done. Used in tests.

push_screen method

def push_screen(self, screen, callback=None):

Push a new screen on the screen stack, making it the current screen.

Parameters

Name	Type	Description	Default
screen	Screen[ScreenResultType] | str	A Screen instance or the name of an installed screen.	required
callback	ScreenResultCallbackType[ScreenResultType] | None	An optional callback function that will be called if the screen is dismissed with a result.	None

Returns

Type	Description
AwaitMount	An optional awaitable that awaits the mounting of the screen and its children.

refresh_css method

def refresh_css(self, animate=True):

Refresh CSS.

Parameters

Name	Type	Description	Default
animate	bool	Also execute CSS animations.	True

remove_mode method

def remove_mode(self, mode):

Removes a mode from the app.

Screens that are running in the stack of that mode are scheduled for pruning.

Parameters

Name	Type	Description	Default
mode	str	The mode to remove. It can't be the active mode.	required

Raises

Type	Description
ActiveModeError	If trying to remove the active mode.
UnknownModeError	If trying to remove an unknown mode.

run method

def run(self, *, headless=False, size=None, auto_pilot=None):

Run the app.

Parameters

Name	Type	Description	Default
headless	bool	Run in headless mode (no output).	False
size	tuple[int, int] | None	Force terminal size to (WIDTH, HEIGHT), or None to auto-detect.	None
auto_pilot	AutopilotCallbackType | None	An auto pilot coroutine.	None

Returns

Type	Description
ReturnType | None	App return value.

run_action async

def run_action(self, action, default_namespace=None):

Perform an action.

Actions are typically associated with key bindings, where you wouldn't need to call this method manually.

Parameters

Name	Type	Description	Default
action	str | ActionParseResult	Action encoded in a string.	required
default_namespace	object | None	Namespace to use if not provided in the action, or None to use app.	None

Returns

Type	Description
bool	True if the event has been handled.

run_async async

def run_async(
    self, *, headless=False, size=None, auto_pilot=None
):

Run the app asynchronously.

Parameters

Name	Type	Description	Default
headless	bool	Run in headless mode (no output).	False
size	tuple[int, int] | None	Force terminal size to (WIDTH, HEIGHT), or None to auto-detect.	None
auto_pilot	AutopilotCallbackType | None	An auto pilot coroutine.	None

Returns

Type	Description
ReturnType | None	App return value.

run_test async

def run_test(
    self,
    *,
    headless=True,
    size=(80, 24),
    tooltips=False,
    notifications=False,
    message_hook=None
):

An asynchronous context manager for testing apps.

Tip

See the guide for testing Textual apps.

Use this to run your app in "headless" mode (no output) and drive the app via a Pilot object.

Example

async with app.run_test() as pilot:
    await pilot.click("#Button.ok")
    assert ...

Parameters

Name	Type	Description	Default
headless	bool	Run in headless mode (no output or input).	True
size	tuple[int, int] | None	Force terminal size to (WIDTH, HEIGHT), or None to auto-detect.	(80, 24)
tooltips	bool	Enable tooltips when testing.	False
notifications	bool	Enable notifications when testing.	False
message_hook	Callable[[Message], None] | None	An optional callback that will called with every message going through the app.	None

save_screenshot method

def save_screenshot(
    self, filename=None, path="./", time_format=None
):

Save an SVG screenshot of the current screen.

Parameters

Name	Type	Description	Default
filename	str | None	Filename of SVG screenshot, or None to auto-generate a filename with the date and time.	None
path	str	Path to directory for output. Defaults to current working directory.	'./'
time_format	str | None	Date and time format to use if filename is None. Defaults to a format like ISO 8601 with some reserved characters replaced with underscores.	None

Returns

Type	Description
str	Filename of screenshot.

set_focus method

def set_focus(self, widget, scroll_visible=True):

Focus (or unfocus) a widget. A focused widget will receive key events first.

Parameters

Name	Type	Description	Default
widget	Widget | None	Widget to focus.	required
scroll_visible	bool	Scroll widget in to view.	True

stop_animation async

def stop_animation(self, attribute, complete=True):

Stop an animation on an attribute.

Parameters

Name	Type	Description	Default
attribute	str	Name of the attribute whose animation should be stopped.	required
complete	bool	Should the animation be set to its final value?	True

Note

If there is no animation scheduled or running, this is a no-op.

switch_mode method

def switch_mode(self, mode):

Switch to a given mode.

Parameters

Name	Type	Description	Default
mode	str	The mode to switch to.	required

Raises

Type	Description
UnknownModeError	If trying to switch to an unknown mode.

switch_screen method

def switch_screen(self, screen):

Switch to another screen by replacing the top of the screen stack with a new screen.

Parameters

Name	Type	Description	Default
screen	Screen | str	Either a Screen object or screen name (the name argument when installed).	required

uninstall_screen method

def uninstall_screen(self, screen):

Uninstall a screen.

If the screen was not previously installed then this method is a null-op. Uninstalling a screen allows Textual to delete it when it is popped or switched. Note that uninstalling a screen is only required if you have previously installed it with install_screen. Textual will also uninstall screens automatically on exit.

Parameters

Name	Type	Description	Default
screen	Screen | str	The screen to uninstall or the name of a installed screen.	required

Returns

Type	Description
str | None	The name of the screen that was uninstalled, or None if no screen was uninstalled.

update_styles method

def update_styles(self, node):

Immediately update the styles of this node and all descendant nodes.

Should be called whenever CSS classes / pseudo classes change. For example, when you hover over a button, the :hover pseudo class will be added, and this method is called to apply the corresponding :hover styles.

validate_sub_title method

def validate_sub_title(self, sub_title):

Make sure the sub-title is set to a string.

validate_title method

def validate_title(self, title):

Make sure the title is set to a string.

watch_dark method

def watch_dark(self, dark):

Watches the dark bool.

This method handles the transition between light and dark mode when you change the dark attribute.

AppError class

Bases: Exception

Base class for general App related exceptions.

InvalidModeError class

Bases: ModeError

Raised if there is an issue with a mode name.

ModeError class

Bases: Exception

Base class for exceptions related to modes.

ScreenError class

Bases: Exception

Base class for exceptions that relate to screens.

ScreenStackError class

Bases: ScreenError

Raised when trying to manipulate the screen stack incorrectly.

UnknownModeError class

Bases: ModeError

Raised when attempting to use a mode that is not known.