Textual 0.38.0 adds a syntax aware TextArea

This is the second big feature release this month after last week's command palette.

The TextArea has finally landed. I know a lot of folk have been waiting for this one. Textual's TextArea is a fully-featured widget for editing code, with syntax highlighting and line numbers. It is highly configurable, and looks great.

Darren Burns (the author of this widget) has penned a terrific write-up on the TextArea. See Things I learned while building Textual's TextArea for some of the challenges he faced.

Scoped CSS

Another notable feature added in 0.38.0 is scoped CSS. A common gotcha in building Textual widgets is that you could write CSS that impacted styles outside of that widget.

Consider the following widget:

class MyWidget(Widget):
    DEFAULT_CSS = """
    MyWidget {
        height: auto;
        border: magenta;
    }
    Label {
        border: solid green;
    }
    """

    def compose(self) -> ComposeResult:
        yield Label("foo")
        yield Label("bar")

The author has intended to style the labels in that widget by adding a green border. This does work for the widget in question, but (prior to 0.38.0) the Label rule would style all Labels (including any outside of the widget) — which was probably not intended.

With version 0.38.0, the CSS is scoped so that only the widget's labels will be styled. This is almost always what you want, which is why it is enabled by default. If you do want to style something outside of the widget you can set SCOPED_CSS=False (as a classvar).

Light and Dark pseudo selectors

We've also made a slight quality of life improvement to the CSS, by adding :light and :dark pseudo selectors. This allows you to change styles depending on whether you have dark mode enabled or not.

This was possible before, just a little verbose. Here's how you would do it in 0.37.0:

App.-dark-mode MyWidget Label {
    ...
}

In 0.38.0 it's a little more concise and readable:

MyWidget:dark Label {
    ...
}

Testing guide

Not strictly part of the release, but we've added a guide on testing Textual apps.

As you may know, we are on a mission to make TUIs a serious proposition for critical apps, which makes testing essential. We've extracted and documented our internal testing tools, including our snapshot tests pytest plugin pytest-textual-snapshot.

This gives devs powerful tools to ensure the quality of their apps. Let us know your thoughts on that!

Release notes

See the release page for the full details on this release.

What's next?

There's lots of features planned over the next few months. One feature I am particularly excited by is a widget to generate plots by wrapping the awesome Plotext library. Check out some early work on this feature:

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