how to capture log data in QTextEdit

[Florian Bruhin]

Hey Stefan,

On Sun, Feb 21, 2021 at 11:41:58AM -0500, Stefan Seefeld wrote:
> I'm trying to capture ("redirect") log data generated by a wrapped C++
> library to a QTextEdit. The internet is full of related questions, but I
> couldn't quite find a working example that matches my needs. I can configure
> my logger to either write to the console (stdout) or to a file, so what I'm
> looking for is a mechanism to attach a "listener" to the given file
> descriptor and let it emit a `readyRead` signal whenever data are available.
> For a reason I don't entirely understand, the `QFile` class does *not* emit
> that signal, and thus is unfortunately unsuitable for this.

I'm not sure why either, but FWIW that behavior is documented as well:
https://doc.qt.io/qt-5/qfile.html#signals

> So, does PyQt5 offer any classes that are equipped to listen to data being
> written to a file descriptor such that I could read them asynchronously ?
> The only examples I could find involve (tcp or udp) sockets or serial ports,
> but not simple files...

Despite the name, QSocketNotifier might work:
https://doc.qt.io/qt-5/qsocketnotifier.html
("Although the class is called QSocketNotifier, it is normally used for
other types of devices than sockets")

Here's an example using it on a Unix FIFO:
https://github.com/qutebrowser/qutebrowser/blob/v2.0.2/qutebrowser/commands/userscripts.py#L38-L92

I'm not sure if I've ever tried it on an ordinary file, though.


Alternatively, maybe a QFileSystemWatcher would work:
https://doc.qt.io/qt-5/qfilesystemwatcher.html

Here's an example:
https://github.com/qutebrowser/qutebrowser/blob/v2.0.2/qutebrowser/misc/editor.py#L62
https://github.com/qutebrowser/qutebrowser/blob/v2.0.2/qutebrowser/misc/editor.py#L194-L201

Florian

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