Allow redirecting App.log and textual.log to a TextLog widget

[liancheng]

While porting some CLI apps to Textual, the TextLog widget can be very useful for showing the logging output of the original CLI app. App.log and textual.log only writes to the devtool, which is helpful for debugging but don't show user-facing info level logs. It would be cool if we can have an easy way to write log messages to a TextLog widget transparently using App.log or textual.log. This will also make migrating some CLI apps easier, as you don't need to pass a reference to the TextLog widget to the legacy CLI business logic code issuing all the logs.

[eliotb]

This is something I ported from an old tkinter app. I doubt it is idiomatic Textual - I'd love to hear from Textual experts what the best way to do this is!

Create a texthandler that keeps a reference to your textlog widget

class TextHandler(logging.Handler):
    """Class for  logging to a TextLog widget"""

    def __init__(self, textlog):
        # run the regular Handler __init__
        logging.Handler.__init__(self)
        # Store a reference to the Text it will log to
        self.text = textlog

    def emit(self, record):
        msg = self.format(record)
        style = "red"
        # style your output depending on e.g record.levelno here
        self.text.write(Text(msg, style))

Connect it up in the App's on_ready

    def on_ready():
        ...
        text_log = self.query_one(TextLog)

        logger = logging.getLogger("test")
        logger.setLevel(logging.DEBUG)
        th = TextHandler(text_log)
        th.setLevel(logging.DEBUG)
        logger.addHandler(th)

Use it somewhere, output will appear in the TextLog

        log = logging.getLogger("test")
        log.info("Something interesting happened")