I am not sure you shouldpass the exceptions silently.

I'm not sure what to report, otherwise. Passing on the FileNotFoundError feels right to me.

I could drop catching CalledProcessError?

You could use shutil.which to determine if xdg-settings exists before trying to call it (LBYL). But here ignoring the exception (EAFP) seems right to me.

With a_preferred_browsers set, this would become:

try:    cmd = "xdg-settings get default-web-browser".split()    _xdg_default_browser = subprocess.check_output(cmd).decode().strip()except (FileNotFoundError, subprocess.CalledProcessError):     passelse:    _preferred_browsers.add(_xdg_default_browser)

I believe that would be more self-explanatory as to the purpose of ignoring the exceptions here (if we fail to find the xdg default browser, we simply don't add it to the preferred browser set)

I wonder if it’s good to change the signature here. Is it impossible to give high priority to the browser found with xdg-settings, if any, with the update_tryorder param?

I took the opportunity to make what I thought was an improvement. The tri-state definition of the old parameter seemed a bit clumsy and unnecessary (note that it was left out of the documentation).

I can back out the change to update_tryorder if it is deemed appropriate.

I'd suggest making the parameterpreferred rather thanpriority and making it keyword-only.

Rather than only allowing a single preferred browser, perhaps it would make sense to make this a_preferred_browsers set? That would have a ripple effect on the other updates below.

My original implementation did this, but I didn't find the enhancement useful. There weren't any ripples.

That said, I'll make the change if this is considered a blocker.

With a set, this condition would becomeif priority or name in _preferred_browsers:

'preferred' is a better name. I'll make the change.

I had managed to make it to this point without encountering the keyword-only concept in the library (or elsewhere, for that matter). Would this cause unnecessary confusion?

Note that 'name in _preferred_browsers' is not enough. xdg-settings returns e.g. 'firefox.desktop'.

keyword-only is our preferred approach to handling boolean arguments in Python 3, as otherwise you end up with code that's ambiguous at the point of calling (as here, where theTrue conveys no info to a reader that doesn't already know the signature, whilepreferred=True is a lot more descriptive)

Regarding_preferred_browser potentially needing to match things likefirefox againstfirefox.desktop, that belongs in an explanatory comment in the code itself. I'm fine with dropping the idea of switching to a set, though.

A slight name tweak may help convey the difference between this field and the new parameter toregister though: what do you think about renaming it to_os_preferred_browser?

With a_preferred_browsers set, this would become:

try:    cmd = "xdg-settings get default-web-browser".split()    _xdg_default_browser = subprocess.check_output(cmd).decode().strip()except (FileNotFoundError, subprocess.CalledProcessError):     passelse:    _preferred_browsers.add(_xdg_default_browser)

I believe that would be more self-explanatory as to the purpose of ignoring the exceptions here (if we fail to find the xdg default browser, we simply don't add it to the preferred browser set)

I'd suggest making the parameterpreferred rather thanpriority and making it keyword-only.

With the above suggested change to the signature ofregister, this and the other options below would become:

register("safari", None, MacOSXOSAScript('safari'), preferred=True)

I'll add the 'else' construct.