The D-Bus library is a messaging library used by various desktop environments (GNOME, KDE, etc) for interprocess communication.

There are multiple Python bindings for DBus:

• GDbus and QtDbus are wrappers over the C/C++ APIs of GLib and Qt

• pydbus is a modern, pythonic API with the goal of being as invisible a layer between the exported API and its user as possible

• dasbus is a Python3-only alternative to pydbus with additional features and better flexibility

• dbus-python is a legacy API, built with a deprecated dbus-glib library, and involving a lot of type-guessing (despite "explicit is better than implicit" and "resist the temptation to guess").

• txdbus is a native Python implementation of the D-Bus protocol for the Twisted networking framework.

• dbus-next is a native Python library for D-Bus with support for multiple IO backends suitable for GUI develeopment and cross platform projects.

See also: DBusBindings on Freedesktop wiki.

The dbus-viewer and qdbusviewer programs let you browse through the services and interfaces available on your system.

pydbus

For more information see pydbus's Readme.

Introspection

from pydbus import SessionBus
bus = SessionBus()

# Create an object that will proxy for a particular remote object.
remote_object = bus.get(
    "org.freedesktop.DBus", # Bus name
    "/org/freedesktop/DBus" # Object path
)

# Introspection returns an XML document containing information
# about the methods supported by an interface.
print("Introspection data:\n")
print(remote_object.Introspect())

Output:

Introspection data:

<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
"http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
<node>
  <interface name="org.freedesktop.DBus.Introspectable">
    <method name="Introspect">
      <arg name="data" direction="out" type="s"/>
    </method>
  </interface>
  <interface name="org.freedesktop.DBus">
    <method name="RequestName">
      <arg direction="in" type="s"/>
      <arg direction="in" type="u"/>
      <arg direction="out" type="u"/>
    </method>
 ...

Calling an interface method

After executing the introspection example:

print(remote_object.ListNames())

Output:

['org.freedesktop.DBus', 'org.freedesktop.Notifications', 'org.freedesktop.PowerManagement', ':1.8', ':1.9', 'org.kde.kaccess', 'org.kde.kded', 'org.kde.StatusNotifierItem-655-1', 'org.freedesktop.systemd1', 'org.ktorrent.ktorrent', 'org.kde.StatusNotifierItem-656-1', 'org.kde.konversation', 'org.pulseaudio.Server', 'org.kde.KScreen', 'org.kde.krunner', 'org.kde.konsole', ':1.40', 'org.a11y.Bus', ':1.41', ':1.42', ':1.20', ':1.43', 'org.kde.klauncher5', ':1.21', ':1.23', 'org.kde.dolphin-3012', 'org.freedesktop.PowerManagement.Inhibit', 'org.kde.Solid.PowerManagement', ':1.24', ':1.25', ':1.49', 'org.kde.kmix', 'org.kde.screensaver', 'org.kde.KWin', 'org.bluez.obex', ':1.29', 'ca.desrt.dconf', 'org.kde.kgpg', 'org.freedesktop.ScreenSaver', 'org.kde.plasmashell', 'org.kde.plasmanetworkmanagement', 'org.kde.StatusNotifierItem-666-1', 'org.kde.kglobalaccel', 'org.freedesktop.FileManager1', 'org.kde.kwalletd5', 'org.PulseAudio1', 'org.kde.polkit-kde-authentication-agent-1', ':1.93', 'org.kde.kded5', 'org.kde.ActivityManager', 'org.kde.keyboard', 'org.kde.kate-3030', ':1.31', 'org.kde.kuiserver', ':1.32', ':1.55', ':1.33', ':1.11', 'org.kde.kwin.Screenshot', ':1.56', ':1.34', 'org.kde.StatusNotifierWatcher', 'org.kde.JobViewServer', ':1.35', ':1.0', ':1.13', ':1.58', 'org.kde.StatusNotifierHost-616', ':1.14', ':1.59', ':1.15', ':1.38', ':1.16', 'org.kde.ksmserver', ':1.39', ':1.17', ':1.5', 'org.kde.Solid.PowerManagement.PolicyAgent', ':1.18', 'org.kde.klauncher', ':1.6', ':1.19']

The following example makes your system hibernate:

# Get the power management object
power = bus.get('org.gnome.PowerManager', '/org/gnome/PowerManager')

# Hibernate the system
if power.CanHibernate():
    power.Hibernate()

dasbus

For more information see dasbus's documentation.

Introspection of a remote object

Introspection returns an XML string containing information about interfaces, methods, properties and signals of the remote object.

from dasbus.connection import SessionMessageBus
bus = SessionMessageBus()

# Create an object that will be a proxy for a particular remote object.
remote_object = bus.get_proxy(
    "org.freedesktop.DBus",  # The bus name
    "/org/freedesktop/DBus"  # The object path
)

# Call the Introspect method of the remote object.
print(remote_object.Introspect())

Accessing a remote property

The following example prints the current hostname.

from dasbus.connection import SystemMessageBus
bus = SystemMessageBus()

proxy = bus.get_proxy(
    "org.freedesktop.hostname1",
    "/org/freedesktop/hostname1"
)

print(proxy.Hostname)

Calling a remote method

The following example sends a notification to the notification server.

from dasbus.connection import SessionMessageBus
bus = SessionMessageBus()

proxy = bus.get_proxy(
    "org.freedesktop.Notifications",
    "/org/freedesktop/Notifications"
)

id = proxy.Notify(
    "", 0, "face-smile", "My notification",
    "Hello World!", [], {}, 0
)

print("The notification {} was sent.".format(id))

dbus-next

For more information see dbus-next's documentation.

The client interface

To use a service on the bus, the library constructs a proxy object you can use to call methods, get and set properties, and listen to signals.

This example connects to a media player and controls it with the MPRIS DBus interface using python's asyncio backend.

   1 from dbus_next.aio import MessageBus
   2 
   3 import asyncio
   4 
   5 loop = asyncio.get_event_loop()
   6 
   7 
   8 async def main():
   9     bus = await MessageBus().connect()
  10     # the introspection xml would normally be included in your project, but
  11     # this is convenient for development
  12     introspection = await bus.introspect('org.mpris.MediaPlayer2.vlc', '/org/mpris/MediaPlayer2')
  13 
  14     obj = bus.get_proxy_object('org.mpris.MediaPlayer2.vlc', '/org/mpris/MediaPlayer2', introspection)
  15     player = obj.get_interface('org.mpris.MediaPlayer2.Player')
  16     properties = obj.get_interface('org.freedesktop.DBus.Properties')
  17 
  18     # call methods on the interface (this causes the media player to play)
  19     await player.call_play()
  20 
  21     volume = await player.get_volume()
  22     print(f'current volume: {volume}, setting to 0.5')
  23 
  24     await player.set_volume(0.5)
  25 
  26     # listen to signals
  27     def on_properties_changed(interface_name, changed_properties, invalidated_properties):
  28         for changed, variant in changed_properties.items():
  29             print(f'property changed: {changed} - {variant.value}')
  30 
  31     properties.on_properties_changed(on_properties_changed)
  32 
  33     await loop.create_future()
  34 
  35 loop.run_until_complete(main())

The service interface

To define a service on the bus, use the ServiceInterface class and decorate class methods to specify DBus methods, properties, and signals with their type signatures.

   1 from dbus_next.service import ServiceInterface, method, dbus_property, signal, Variant
   2 from dbus_next.aio MessageBus
   3 
   4 import asyncio
   5 
   6 class ExampleInterface(ServiceInterface):
   7     def __init__(self, name):
   8         super().__init__(name)
   9         self._string_prop = 'kevin'
  10 
  11     @method()
  12     def Echo(self, what: 's') -> 's':
  13         return what
  14 
  15     @method()
  16     def GetVariantDict() -> 'a{sv}':
  17         return {
  18             'foo': Variant('s', 'bar'),
  19             'bat': Variant('x', -55),
  20             'a_list': Variant('as', ['hello', 'world'])
  21         }
  22 
  23     @dbus_property()
  24     def string_prop(self) -> 's':
  25         return self._string_prop
  26 
  27     @string_prop.setter
  28     def string_prop_setter(self, val: 's'):
  29         self._string_prop = val
  30 
  31     @signal()
  32     def signal_simple(self) -> 's':
  33         return 'hello'
  34 
  35 async def main():
  36     bus = await MessageBus().connect()
  37     interface = ExampleInterface('test.interface')
  38     bus.export('/test/path', interface)
  39     # now that we are ready to handle requests, we can request name from D-Bus
  40     await bus.request_name('test.name')
  41     # wait indefinitely
  42     await asyncio.get_event_loop().create_future()
  43 
  44 asyncio.get_event_loop().run_until_complete(main())