Devtools¶
Note
If you don't have the textual
command on your path, you may have forgotten to install with the dev
switch.
See getting started for details.
Textual comes with a command line application of the same name. The textual
command is a super useful tool that will help you to build apps.
Take a moment to look through the available sub-commands. There will be even more helpful tools here in the future.
Run¶
You can run Textual apps with the run
subcommand. If you supply a path to a Python file it will load and run the application.
The run
sub-command will first look for a App
instance called app
in the global scope of your Python file. If there is no app
, it will create an instance of the first App
class it finds and run that.
Alternatively, you can add the name of an App
instance or class after a colon to run a specific app in the Python file. Here's an example:
Note
If the Python file contains a call to app.run() then you can launch the file as you normally would any other Python program. Running your app via textual run
will give you access to a few Textual features such as live editing of CSS files.
Live editing¶
If you combine the run
command with the --dev
switch your app will run in development mode.
One of the features of dev mode is live editing of CSS files: any changes to your CSS will be reflected in the terminal a few milliseconds later.
This is a great feature for iterating on your app's look and feel. Open the CSS in your editor and have your app running in a terminal. Edits to your CSS will appear almost immediately after you save.
Console¶
When building a typical terminal application you are generally unable to use print
when debugging (or log to the console). This is because anything you write to standard output will overwrite application content. Textual has a solution to this in the form of a debug console which restores print
and adds a few additional features to help you debug.
To use the console, open up two terminal emulators. Run the following in one of the terminals:
You should see the Textual devtools welcome message:
In the other console, run your application with textual run
and the --dev
switch:
Anything you print
from your application will be displayed in the console window. Textual will also write log messages to this window which may be helpful when debugging your application.
Verbosity¶
Textual writes log messages to inform you about certain events, such as when the user presses a key or clicks on the terminal. To avoid swamping you with too much information, some events are marked as "verbose" and will be excluded from the logs. If you want to see these log messages, you can add the -v
switch.
Textual log¶
In addition to simple strings, Textual console supports Rich formatting. To write rich logs, import log
as follows:
This method will pretty print data structures (like lists and dicts) as well as Rich renderables. Here are some examples:
log("Hello, World") # simple string
log(locals()) # Log local variables
log(children=self.children, pi=3.141592) # key/values
log(self.tree) # Rich renderables
Textual log messages may contain console Markup:
Log method¶
There's a convenient shortcut to log
available on the App
and Widget
objects. This is useful in event handlers. Here's an example: