Dbus Tutorial GObject Introspection instead of python dbus
Introduction
Introspection
Network Manager
Create a Service
GObject Introspection
In previous posts, I have looked at using the python-dbus to communicate with other processes, essentially using it the same way we use the dbus-send command.
There is another way to create DBus messages. Its a bit more complicated than python-dbus, and it depends upon Gnome, but its also more robust and perhaps better maintained.
Using Gobject Introspection replacement for python-dbus is described several places, but the best example is here. Python-dbus as a separate bindings project has also suffered with complaints of "lightly maintained," and an awkward method of exposing properties that has been unfixed for years.
These examples only work for clients. Gnome Bug #656330 shows that services cannot yet use PyGI.
Heres an example notification using Pygi instead of Python-DBus. Its based on this blog post by Martin Pitt, but expanded a bit to show all the variables I can figure out....
1) Header and load gi#!/usr/bin/env python3
import gi.repository
from gi.repository import Gio, GLib
2) Connect to the DBus Session BusDocumentation: http://developer.gnome.org/gio/2.29/GDBusConnection.html
session_bus = Gio.BusType.SESSION
cancellable = None
connection = Gio.bus_get_sync(session_bus, cancellable)
3) Create (but dont send) the DBus message headerDocumentation: http://developer.gnome.org/gio/2.29/GDBusProxy.html
proxy_property = 0
interface_properties_array = None
destination = org.freedesktop.Notifications
path = /org/freedesktop/Notifications
interface = destination
notify = Gio.DBusProxy.new_sync(
connection,
proxy_property,
interface_properties_array,
destination,
path,
interface,
cancellable)
4) Create (but dont send) the DBus message dataThe order is determined by arg order of the Notification system
Documentation: http://developer.gnome.org/notification-spec/#protocol
application_name = test
title = Hello World!
body_text = Subtext
id_num_to_replace = 0
actions_list = []
hints_dict = {}
display_milliseconds = 5000
icon = gtk-ok # Can use full path, too /usr/share/icons/Humanity/actions/
args = GLib.Variant((susssasa{sv}i), (
application_name,
id_num_to_replace,
icon,
title,
body_text,
actions_list,
hints_dict,
display_milliseconds))
5) Send the DBus message header and data to the notification serviceDocumentation: http://developer.gnome.org/gio/2.29/GDBusProxy.html
method = Notify
timeout = -1
result = notify.call_sync(method, args, proxy_property, timeout, cancellable)
6) (Optional) Convert the result value from a Uint32 to a python integerid = result.unpack()[0]
print(id)
Play with it a bit, and you will quickly see how the pieces work together.
Here is a different, original example DBus client using introspection and this askubuntu question. You can see this is a modified and simplified version of the above example:
#!/usr/bin/env python3
import gi.repository
from gi.repository import Gio, GLib
# Create the DBus message
destination = org.freedesktop.NetworkManager
path = /org/freedesktop/NetworkManager
interface = org.freedesktop.DBus.Introspectable
method = Introspect
args = None
answer_fmt = GLib.VariantType.new ((v))
proxy_prpty = Gio.DBusCallFlags.NONE
timeout = -1
cancellable = None
# Connect to DBus, send the DBus message, and receive the reply
bus = Gio.bus_get_sync(Gio.BusType.SYSTEM, None)
reply = bus.call_sync(destination, path, interface,
method, args, answer_fmt,
proxy_prpty, timeout, cancellable)
# Convert the result value to a formatted python element
print(reply.unpack()[0])
Here is a final DBus client example, getting the properties of the current Network Manager connection
#!/usr/bin/env python3
import gi.repository
from gi.repository import Gio, GLib
# Create the DBus message
destination = org.freedesktop.NetworkManager
path = /org/freedesktop/NetworkManager/ActiveConnection/19
interface = org.freedesktop.DBus.Properties
method = GetAll
args = GLib.Variant((ss),
(org.freedesktop.NetworkManager.Connection.Active, None))
answer_fmt = GLib.VariantType.new ((v))
proxy_prpty = Gio.DBusCallFlags.NONE
timeout = -1
cancellable = None
# Connect to DBus, send the DBus message, and receive the reply
bus = Gio.bus_get_sync(Gio.BusType.SYSTEM, None)
reply = bus.call_sync(destination, path, interface,
method, args, answer_fmt,
proxy_prpty, timeout, cancellable)
# Convert the result value to a useful python object and print
[print(item[0], item[1]) for item in result.unpack()[0].items()]
As you can see from this example, dbus communication is actually pretty easy using GLib: Assign the nine variables, turn the crank, and unpack the result.
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