Command Palette¶
Textual apps have a built-in command palette, which gives users a quick way to access certain functionality within your app.
In this chapter we will explain what a command palette is, how to use it, and how you can add your own commands.
Launching the command palette¶
Press Ctrl+P to invoke the command palette screen, which contains of a single input widget. Textual will suggest commands as you type in that input. Press Up or Down to select a command from the list, and Enter to invoke it.
Commands are looked up via a fuzzy search, which means Textual will show commands that match the keys you type in the same order, but not necessarily at the start of the command. For instance the "Change theme" command will be shown if you type "ch" (for change), but you could also type "th" (to match theme). This scheme allows the user to quickly get to a particular command with fewer key-presses.
System commands¶
Textual apps have a number of system commands enabled by default.
These are declared in the App.get_system_commands method.
You can implement this method in your App class to add more commands.
To declare a command, define a get_system_commands method on your App.
Textual will call this method with the screen that was active when the user summoned the command palette.
You can add a command by yielding a SystemCommand object which contains title and help text to be shown in the command palette, and callback which is a callable to run when the user selects the command.
Additionally, there is a discover boolean which when True (the default) shows the command even if the search import is empty. When set to False, the command will show only when there is input.
Here's how we would add a command to ring the terminal bell (a super useful piece of functionality):
from typing import Iterable
from textual.app import App, SystemCommand
from textual.screen import Screen
class BellCommandApp(App):
"""An app with a 'bell' command."""
def get_system_commands(self, screen: Screen) -> Iterable[SystemCommand]:
yield from super().get_system_commands(screen) # (1)!
yield SystemCommand("Bell", "Ring the bell", self.bell) # (2)!
if __name__ == "__main__":
app = BellCommandApp()
app.run()
- Adds the default commands from the base class.
- Adds a new command.
This is a straightforward way of adding commands to your app. For more advanced integrations you can implement your own command providers.
Command providers¶
To add your own command(s) to the command palette, define a command.Provider class then add it to the COMMANDS class var on your App class.
Let's look at a simple example which adds the ability to open Python files via the command palette.
The following example will display a blank screen initially, but if you bring up the command palette and start typing the name of a Python file, it will show the command to open it.
Tip
If you are running that example from the repository, you may want to add some additional Python files to see how the examples works with multiple files.
from __future__ import annotations
from functools import partial
from pathlib import Path
from textual.app import App, ComposeResult
from textual.command import Hit, Hits, Provider
from textual.containers import VerticalScroll
from textual.widgets import Static
class PythonFileCommands(Provider):
"""A command provider to open a Python file in the current working directory."""
def read_files(self) -> list[Path]:
"""Get a list of Python files in the current working directory."""
return list(Path("./").glob("*.py"))
async def startup(self) -> None: # (1)!
"""Called once when the command palette is opened, prior to searching."""
worker = self.app.run_worker(self.read_files, thread=True)
self.python_paths = await worker.wait()
async def search(self, query: str) -> Hits: # (2)!
"""Search for Python files."""
matcher = self.matcher(query) # (3)!
app = self.app
assert isinstance(app, ViewerApp)
for path in self.python_paths:
command = f"open {str(path)}"
score = matcher.match(command) # (4)!
if score > 0:
yield Hit(
score,
matcher.highlight(command), # (5)!
partial(app.open_file, path),
help="Open this file in the viewer",
)
class ViewerApp(App):
"""Demonstrate a command source."""
COMMANDS = App.COMMANDS | {PythonFileCommands} # (6)!
def compose(self) -> ComposeResult:
with VerticalScroll():
yield Static(id="code", expand=True)
def open_file(self, path: Path) -> None:
"""Open and display a file with syntax highlighting."""
from rich.syntax import Syntax
syntax = Syntax.from_path(
str(path),
line_numbers=True,
word_wrap=False,
indent_guides=True,
theme="github-dark",
)
self.query_one("#code", Static).update(syntax)
if __name__ == "__main__":
app = ViewerApp()
app.run()
- This method is called when the command palette is first opened.
- Called on each key-press.
- Get a Matcher instance to compare against hits.
- Use the matcher to get a score.
- Highlights matching letters in the search.
- Adds our custom command provider and the default command provider.
There are four methods you can override in a command provider: startup, search, discover and shutdown.
All of these methods should be coroutines (async def). Only search is required, the other methods are optional.
Let's explore those methods in detail.
startup method¶
The startup method is called when the command palette is opened.
You can use this method as way of performing work that needs to be done prior to searching.
In the example, we use this method to get the Python (.py) files in the current working directory.
search method¶
The search method is responsible for finding results (or hits) that match the user's input.
This method should yield Hit objects for any command that matches the query argument.
Exactly how the matching is implemented is up to the author of the command provider, but we recommend using the builtin fuzzy matcher object, which you can get by calling matcher.
This object has a match() method which compares the user's search term against the potential command and returns a score.
A score of zero means no hit, and you can discard the potential command.
A score of above zero indicates the confidence in the result, where 1 is an exact match, and anything lower indicates a less confident match.
The Hit contains information about the score (used in ordering) and how the hit should be displayed, and an optional help string.
It also contains a callback, which will be run if the user selects that command.
In the example above, the callback is a lambda which calls the open_file method in the example app.
Note
Unlike most other places in Textual, errors in command provider will not exit the app.
This is a deliberate design decision taken to prevent a single broken Provider class from making the command palette unusable.
Errors in command providers will be logged to the console.
discover method¶
The discover method is responsible for providing results (or discovery hits) that should be shown to the user when the command palette input is empty;
this is to aid in command discoverability.
Note
Because discover hits are shown the moment the command palette is opened, these should ideally be quick to generate;
commands that might take time to generate are best left for search -- use discover to help the user easily find the most important commands.
discover is similar to search but with these differences:
discoveraccepts no parameters (instead of the search value)discoveryields instances ofDiscoveryHit(instead of instances ofHit)
Instances of DiscoveryHit contain information about how the hit should be displayed, an optional help string, and a callback which will be run if the user selects that command.
shutdown method¶
The shutdown method is called when the command palette is closed.
You can use this as a hook to gracefully close any objects you created in startup.
Screen commands¶
You can also associate commands with a screen by adding a COMMANDS class var to your Screen class.
Commands defined on a screen are only considered when that screen is active. You can use this to implement commands that are specific to a particular screen, that wouldn't be applicable everywhere in the app.
Disabling the command palette¶
The command palette is enabled by default.
If you would prefer not to have the command palette, you can set ENABLE_COMMAND_PALETTE = False on your app class.
Here's an app class with no command palette:
Changing command palette key¶
You can change the key that opens the command palette by setting the class variable COMMAND_PALETTE_BINDING on your app.
Prior to version 0.77.0, Textual used the binding ctrl+backslash to launch the command palette.
Here's how you would restore the older key binding: