Question

I tried the code below in interactive python shell and got the follow error in line 3 of code, using D-Feet I see that path and interface exists in bus, and with the command dbus-send I able to get the devices, see in end of this message. Why not work with this code in python? PS: I using ubuntu 12.04, tried too in ubuntu 11, same problem.

Code:

import dbus
bus = dbus.SessionBus()
obj = bus.get_object('org.freedesktop.NetworkManager', '/org/freedesktop/NetworkManager')
t = dbus.Interface(obj, "org.freedesktop.NetworkManager")
t.GetDevices()

Output error entering line 3 of code:

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/usr/lib/pymodules/python2.7/dbus/bus.py", line 244, in get_object
    follow_name_owner_changes=follow_name_owner_changes)
  File "/usr/lib/pymodules/python2.7/dbus/proxies.py", line 241, in __init__
    self._named_service = conn.activate_name_owner(bus_name)
  File "/usr/lib/pymodules/python2.7/dbus/bus.py", line 183, in activate_name_owner
    self.start_service_by_name(bus_name)
  File "/usr/lib/pymodules/python2.7/dbus/bus.py", line 281, in start_service_by_name
    'su', (bus_name, flags)))
  File "/usr/lib/pymodules/python2.7/dbus/connection.py", line 630, in call_blocking
    message, timeout)
DBusException: org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.NetworkManager was not provided
 by any .service files

Shell command that work:

dbus-send --system --print-reply --reply-timeout=2000 --type=method_call --dest=org.freedesktop.NetworkManager /org/freedesktop/NetworkManager org.freedesktop.NetworkManager.GetDevices

Output:

method return sender=:1.2 -> dest=:1.69 reply_serial=2
   array [
      object path "/org/freedesktop/NetworkManager/Devices/0"
   ]

This is just a example, I wish to know why don’t work, If I change line 3 to (note the DBus name in first parameter):

obj = bus.get_object('org.freedesktop.DBus', '/org/freedesktop/NetworkManager')

the error don’t occur, but in this interface the method GetDevices doesn’t exists.

Answer 1

In your command line example you’re asking for the system bus:

dbus-send --system ...

In your Python code, you’re asking for the session bus:

bus = dbus.SessionBus()

If you try the request over the system bus, I think you’ll find that it works:

>>> import dbus
>>> bus = dbus.SystemBus()
>>> obj = bus.get_object('org.freedesktop.NetworkManager', '/org/freedesktop/NetworkManager')
>>> t = dbus.Interface(obj, "org.freedesktop.NetworkManager")
>>> t.GetDevices()
dbus.Array([dbus.ObjectPath('/org/freedesktop/NetworkManager/Devices/0'), dbus.ObjectPath('/org/freedesktop/NetworkManager/Devices/1')], signature=dbus.Signature('o'))
>>>