Doc or examples don't include handling of dbus method errors

[pespin]

In Dbus methods can return errors instead of returning expected value. I could not find simple example or good documentation on how to handle them. A simple example showing how to handle common errors should be provided, as well as adding a paragraph in the documentation/tutorial.

For instance, from ofono https://git.kernel.org/pub/scm/network/ofono/ofono.git/tree/doc/network-api.txt:

		void Register()

			Attempts to register to the default network. The
			default network is normally selected by the settings
			from the SIM card.

			Possible Errors: [service].Error.InProgress
					 [service].Error.NotImplemented
					 [service].Error.Failed
					 [service].Error.AccessDenied

And I got this stack trace today:

    dbus_op.Register()
  File "/usr/local/lib/python3.4/dist-packages/pydbus/proxy_method.py", line 75, in __call__
    0, timeout_to_glib(timeout), None).unpack()
GLib.Error: g-io-error-quark: GDBus.Error:org.ofono.Error.InProgress: Operation already in progress (36)

For now I'll try to do something like this, but it's still not clear to me whether this is correct or not:

        try:
            netreg.Register()
        except org.ofono.Error.InProgress as e:
            self.log('Register already in progress', e)

[pespin]

For reference, I'm finally doing something like this now. Still not checked it's correct as I cannot reproduce the exception:

    try:
        method()
    except Exception as e:
        if isinstance(e, GLib.Error) and err_str in e.domain:
            return
        raise e

[Hegz]

I ended up with:

from gi.repository.GLib import GError

...

try:
  thing()
except GError as e:
  if 'dbus.Error.Name' in str(e.args):
    print('Deal with this error')
  else:
    raise e

still learning python, so not sure if that's right, but it is handling the exception.

[jlucier]

This is probably useful as reference: https://pygobject.readthedocs.io/en/latest/guide/api/error_handling.html