# Copyright (C) 2003-2006 Red Hat Inc. <http://www.redhat.com/>
# Copyright (C) 2003 David Zeuthen
# Copyright (C) 2004 Rob Taylor
# Copyright (C) 2005-2006 Collabora Ltd. <http://www.collabora.co.uk/>
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation
# files (the "Software"), to deal in the Software without
# restriction, including without limitation the rights to use, copy,
# modify, merge, publish, distribute, sublicense, and/or sell copies
# of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
# HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
# WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
# DEALINGS IN THE SOFTWARE.
__all__ = ('BusName', 'Object', 'FallbackObject', 'method', 'signal')
__docformat__ = 'restructuredtext'
import sys
import logging
import threading
import traceback
from collections import Sequence
import _dbus_bindings
from dbus import (
INTROSPECTABLE_IFACE, ObjectPath, SessionBus, Signature, Struct,
validate_bus_name, validate_object_path)
from dbus.decorators import method, signal
from dbus.exceptions import (
DBusException, NameExistsException, UnknownMethodException)
from dbus.lowlevel import ErrorMessage, MethodReturnMessage, MethodCallMessage
from dbus.proxies import LOCAL_PATH
from dbus._compat import is_py2
_logger = logging.getLogger('dbus.service')
class _VariantSignature(object):
"""A fake method signature which, when iterated, yields an endless stream
of 'v' characters representing variants (handy with zip()).
It has no string representation.
"""
def __iter__(self):
"""Return self."""
return self
def __next__(self):
"""Return 'v' whenever called."""
return 'v'
if is_py2:
next = __next__
class BusName(object):
"""A base class for exporting your own Named Services across the Bus.
When instantiated, objects of this class attempt to claim the given
well-known name on the given bus for the current process. The name is
released when the BusName object becomes unreferenced.
If a well-known name is requested multiple times, multiple references
to the same BusName object will be returned.
Caveats
-------
- Assumes that named services are only ever requested using this class -
if you request names from the bus directly, confusion may occur.
- Does not handle queueing.
"""
def __new__(cls, name, bus=None, allow_replacement=False , replace_existing=False, do_not_queue=False):
"""Constructor, which may either return an existing cached object
or a new object.
:Parameters:
`name` : str
The well-known name to be advertised
`bus` : dbus.Bus
A Bus on which this service will be advertised.
Omitting this parameter or setting it to None has been
deprecated since version 0.82.1. For backwards compatibility,
if this is done, the global shared connection to the session
bus will be used.
`allow_replacement` : bool
If True, other processes trying to claim the same well-known
name will take precedence over this one.
`replace_existing` : bool
If True, this process can take over the well-known name
from other processes already holding it.
`do_not_queue` : bool
If True, this service will not be placed in the queue of
services waiting for the requested name if another service
already holds it.
"""
validate_bus_name(name, allow_well_known=True, allow_unique=False)
# if necessary, get default bus (deprecated)
if bus is None:
import warnings
warnings.warn('Omitting the "bus" parameter to '
'dbus.service.BusName.__init__ is deprecated',
DeprecationWarning, stacklevel=2)
bus = SessionBus()
# see if this name is already defined, return it if so
# FIXME: accessing internals of Bus
if name in bus._bus_names:
return bus._bus_names[name]
# otherwise register the name
name_flags = (
(allow_replacement and _dbus_bindings.NAME_FLAG_ALLOW_REPLACEMENT or 0) |
(replace_existing and _dbus_bindings.NAME_FLAG_REPLACE_EXISTING or 0) |
(do_not_queue and _dbus_bindings.NAME_FLAG_DO_NOT_QUEUE or 0))
retval = bus.request_name(name, name_flags)
# TODO: more intelligent tracking of bus name states?
if retval == _dbus_bindings.REQUEST_NAME_REPLY_PRIMARY_OWNER:
pass
elif retval == _dbus_bindings.REQUEST_NAME_REPLY_IN_QUEUE:
# queueing can happen by default, maybe we should
# track this better or let the user know if they're
# queued or not?
pass
elif retval == _dbus_bindings.REQUEST_NAME_REPLY_EXISTS:
raise NameExistsException(name)
elif retval == _dbus_bindings.REQUEST_NAME_REPLY_ALREADY_OWNER:
# if this is a shared bus which is being used by someone
# else in this process, this can happen legitimately
pass
else:
raise RuntimeError('requesting bus name %s returned unexpected value %s' % (name, retval))
# and create the object
bus_name = object.__new__(cls)
bus_name._bus = bus
bus_name._name = name
# cache instance (weak ref only)
# FIXME: accessing Bus internals again
bus._bus_names[name] = bus_name
return bus_name
# do nothing because this is called whether or not the bus name
# object was retrieved from the cache or created new
def __init__(self, *args, **keywords):
pass
# we can delete the low-level name here because these objects
# are guaranteed to exist only once for each bus name
def __del__(self):
self._bus.release_name(self._name)
pass
def get_bus(self):
"""Get the Bus this Service is on"""
return self._bus
def get_name(self):
"""Get the name of this service"""
return self._name
def __repr__(self):
return '<dbus.service.BusName %s on %r at %#x>' % (self._name, self._bus, id(self))
__str__ = __repr__
def _method_lookup(self, method_name, dbus_interface):
"""Walks the Python MRO of the given class to find the method to invoke.
Returns two methods, the one to call, and the one it inherits from which
defines its D-Bus interface name, signature, and attributes.
"""
parent_method = None
candidate_class = None
successful = False
# split up the cases when we do and don't have an interface because the
# latter is much simpler
if dbus_interface:
# search through the class hierarchy in python MRO order
for cls in self.__class__.__mro__:
# if we haven't got a candidate class yet, and we find a class with a
# suitably named member, save this as a candidate class
if (not candidate_class and method_name in cls.__dict__):
if ("_dbus_is_method" in cls.__dict__[method_name].__dict__
and "_dbus_interface" in cls.__dict__[method_name].__dict__):
# however if it is annotated for a different interface
# than we are looking for, it cannot be a candidate
if cls.__dict__[method_name]._dbus_interface == dbus_interface:
candidate_class = cls
parent_method = cls.__dict__[method_name]
successful = True
break
else:
pass
else:
candidate_class = cls
# if we have a candidate class, carry on checking this and all
# superclasses for a method annoated as a dbus method
# on the correct interface
if (candidate_class and method_name in cls.__dict__
and "_dbus_is_method" in cls.__dict__[method_name].__dict__
and "_dbus_interface" in cls.__dict__[method_name].__dict__
and cls.__dict__[method_name]._dbus_interface == dbus_interface):
# the candidate class has a dbus method on the correct interface,
# or overrides a method that is, success!
parent_method = cls.__dict__[method_name]
successful = True
break
else:
# simpler version of above
for cls in self.__class__.__mro__:
if (not candidate_class and method_name in cls.__dict__):
candidate_class = cls
if (candidate_class and method_name in cls.__dict__
and "_dbus_is_method" in cls.__dict__[method_name].__dict__):
parent_method = cls.__dict__[method_name]
successful = True
break
if successful:
return (candidate_class.__dict__[method_name], parent_method)
else:
if dbus_interface:
raise UnknownMethodException('%s is not a valid method of interface %s' % (method_name, dbus_interface))
else:
raise UnknownMethodException('%s is not a valid method' % method_name)
def _method_reply_return(connection, message, method_name, signature, *retval):
reply = MethodReturnMessage(message)
try:
reply.append(signature=signature, *retval)
except Exception as e:
logging.basicConfig()
if signature is None:
try:
signature = reply.guess_signature(retval) + ' (guessed)'
except Exception as e:
_logger.error('Unable to guess signature for arguments %r: '
'%s: %s', retval, e.__class__, e)
raise
_logger.error('Unable to append %r to message with signature %s: '
'%s: %s', retval, signature, e.__class__, e)
raise
connection.send_message(reply)
def _method_reply_error(connection, message, exception):
name = getattr(exception, '_dbus_error_name', None)
if name is not None:
pass
elif getattr(exception, '__module__', '') in ('', '__main__'):
name = 'org.freedesktop.DBus.Python.%s' % exception.__class__.__name__
else:
name = 'org.freedesktop.DBus.Python.%s.%s' % (exception.__module__, exception.__class__.__name__)
et, ev, etb = sys.exc_info()
if isinstance(exception, DBusException) and not exception.include_traceback:
# We don't actually want the traceback anyway
contents = exception.get_dbus_message()
elif ev is exception:
# The exception was actually thrown, so we can get a traceback
contents = ''.join(traceback.format_exception(et, ev, etb))
else:
# We don't have any traceback for it, e.g.
# async_err_cb(MyException('Failed to badger the mushroom'))
# see also https://bugs.freedesktop.org/show_bug.cgi?id=12403
contents = ''.join(traceback.format_exception_only(exception.__class__,
exception))
reply = ErrorMessage(message, name, contents)
connection.send_message(reply)
class InterfaceType(type):
def __init__(cls, name, bases, dct):
# these attributes are shared between all instances of the Interface
# object, so this has to be a dictionary that maps class names to
# the per-class introspection/interface data
class_table = getattr(cls, '_dbus_class_table', {})
cls._dbus_class_table = class_table
interface_table = class_table[cls.__module__ + '.' + name] = {}
# merge all the name -> method tables for all the interfaces
# implemented by our base classes into our own
for b in bases:
base_name = b.__module__ + '.' + b.__name__
if getattr(b, '_dbus_class_table', False):
for (interface, method_table) in class_table[base_name].items():
our_method_table = interface_table.setdefault(interface, {})
our_method_table.update(method_table)
# add in all the name -> method entries for our own methods/signals
for func in dct.values():
if getattr(func, '_dbus_interface', False):
method_table = interface_table.setdefault(func._dbus_interface, {})
method_table[func.__name__] = func
super(InterfaceType, cls).__init__(name, bases, dct)
# methods are different to signals, so we have two functions... :)
def _reflect_on_method(cls, func):
args = func._dbus_args
if func._dbus_in_signature:
# convert signature into a tuple so length refers to number of
# types, not number of characters. the length is checked by
# the decorator to make sure it matches the length of args.
in_sig = tuple(Signature(func._dbus_in_signature))
else:
# magic iterator which returns as many v's as we need
in_sig = _VariantSignature()
if func._dbus_out_signature:
out_sig = Signature(func._dbus_out_signature)
else:
# its tempting to default to Signature('v'), but
# for methods that return nothing, providing incorrect
# introspection data is worse than providing none at all
out_sig = []
reflection_data = ' <method name="%s">\n' % (func.__name__)
for pair in zip(in_sig, args):
reflection_data += ' <arg direction="in" type="%s" name="%s" />\n' % pair
for type in out_sig:
reflection_data += ' <arg direction="out" type="%s" />\n' % type
reflection_data += ' </method>\n'
return reflection_data
def _reflect_on_signal(cls, func):
args = func._dbus_args
if func._dbus_signature:
# convert signature into a tuple so length refers to number of
# types, not number of characters
sig = tuple(Signature(func._dbus_signature))
else:
# magic iterator which returns as many v's as we need
sig = _VariantSignature()
reflection_data = ' <signal name="%s">\n' % (func.__name__)
for pair in zip(sig, args):
reflection_data = reflection_data + ' <arg type="%s" name="%s" />\n' % pair
reflection_data = reflection_data + ' </signal>\n'
return reflection_data
# Define Interface as an instance of the metaclass InterfaceType, in a way
# that is compatible across both Python 2 and Python 3.
Interface = InterfaceType('Interface', (object,), {})
#: A unique object used as the value of Object._object_path and
#: Object._connection if it's actually in more than one place
_MANY = object()
class Object(Interface):
r"""A base class for exporting your own Objects across the Bus.
Just inherit from Object and mark exported methods with the
@\ `dbus.service.method` or @\ `dbus.service.signal` decorator.
Example::
class Example(dbus.service.object):
def __init__(self, object_path):
dbus.service.Object.__init__(self, dbus.SessionBus(), path)
self._last_input = None
@dbus.service.method(interface='com.example.Sample',
in_signature='v', out_signature='s')
def StringifyVariant(self, var):
self.LastInputChanged(var) # emits the signal
return str(var)
@dbus.service.signal(interface='com.example.Sample',
signature='v')
def LastInputChanged(self, var):
# run just before the signal is actually emitted
# just put "pass" if nothing should happen
self._last_input = var
@dbus.service.method(interface='com.example.Sample',
in_signature='', out_signature='v')
def GetLastInput(self):
return self._last_input
"""
#: If True, this object can be made available at more than one object path.
#: If True but `SUPPORTS_MULTIPLE_CONNECTIONS` is False, the object may
#: handle more than one object path, but they must all be on the same
#: connection.
SUPPORTS_MULTIPLE_OBJECT_PATHS = False
#: If True, this object can be made available on more than one connection.
#: If True but `SUPPORTS_MULTIPLE_OBJECT_PATHS` is False, the object must
#: have the same object path on all its connections.
SUPPORTS_MULTIPLE_CONNECTIONS = False
def __init__(self, conn=None, object_path=None, bus_name=None):
"""Constructor. Either conn or bus_name is required; object_path
is also required.
:Parameters:
`conn` : dbus.connection.Connection or None
The connection on which to export this object.
If None, use the Bus associated with the given ``bus_name``.
If there is no ``bus_name`` either, the object is not
initially available on any Connection.
For backwards compatibility, if an instance of
dbus.service.BusName is passed as the first parameter,
this is equivalent to passing its associated Bus as
``conn``, and passing the BusName itself as ``bus_name``.
`object_path` : str or None
A D-Bus object path at which to make this Object available
immediately. If this is not None, a `conn` or `bus_name` must
also be provided.
`bus_name` : dbus.service.BusName or None
Represents a well-known name claimed by this process. A
reference to the BusName object will be held by this
Object, preventing the name from being released during this
Object's lifetime (unless it's released manually).
"""
if object_path is not None:
validate_object_path(object_path)
if isinstance(conn, BusName):
# someone's using the old API; don't gratuitously break them
bus_name = conn
conn = bus_name.get_bus()
elif conn is None:
if bus_name is not None:
# someone's using the old API but naming arguments, probably
conn = bus_name.get_bus()
#: Either an object path, None or _MANY
self._object_path = None
#: Either a dbus.connection.Connection, None or _MANY
self._connection = None
#: A list of tuples (Connection, object path, False) where the False
#: is for future expansion (to support fallback paths)
self._locations = []
#: Lock protecting `_locations`, `_connection` and `_object_path`
self._locations_lock = threading.Lock()
#: True if this is a fallback object handling a whole subtree.
self._fallback = False
self._name = bus_name
if conn is None and object_path is not None:
raise TypeError('If object_path is given, either conn or bus_name '
'is required')
if conn is not None and object_path is not None:
self.add_to_connection(conn, object_path)
@property
def __dbus_object_path__(self):
"""The object-path at which this object is available.
Access raises AttributeError if there is no object path, or more than
one object path.
Changed in 0.82.0: AttributeError can be raised.
"""
if self._object_path is _MANY:
raise AttributeError('Object %r has more than one object path: '
'use Object.locations instead' % self)
elif self._object_path is None:
raise AttributeError('Object %r has no object path yet' % self)
else:
return self._object_path
@property
def connection(self):
"""The Connection on which this object is available.
Access raises AttributeError if there is no Connection, or more than
one Connection.
Changed in 0.82.0: AttributeError can be raised.
"""
if self._connection is _MANY:
raise AttributeError('Object %r is on more than one Connection: '
'use Object.locations instead' % self)
elif self._connection is None:
raise AttributeError('Object %r has no Connection yet' % self)
else:
return self._connection
@property
def locations(self):
"""An iterable over tuples representing locations at which this
object is available.
Each tuple has at least two items, but may have more in future
versions of dbus-python, so do not rely on their exact length.
The first two items are the dbus.connection.Connection and the object
path.
:Since: 0.82.0
"""
return iter(self._locations)
def add_to_connection(self, connection, path):
"""Make this object accessible via the given D-Bus connection and
object path.
:Parameters:
`connection` : dbus.connection.Connection
Export the object on this connection. If the class attribute
SUPPORTS_MULTIPLE_CONNECTIONS is False (default), this object
can only be made available on one connection; if the class
attribute is set True by a subclass, the object can be made
available on more than one connection.
`path` : dbus.ObjectPath or other str
Place the object at this object path. If the class attribute
SUPPORTS_MULTIPLE_OBJECT_PATHS is False (default), this object
can only be made available at one object path; if the class
attribute is set True by a subclass, the object can be made
available with more than one object path.
:Raises ValueError: if the object's class attributes do not allow the
object to be exported in the desired way.
:Since: 0.82.0
"""
if path == LOCAL_PATH:
raise ValueError('Objects may not be exported on the reserved '
'path %s' % LOCAL_PATH)
self._locations_lock.acquire()
try:
if (self._connection is not None and
self._connection is not connection and
not self.SUPPORTS_MULTIPLE_CONNECTIONS):
raise ValueError('%r is already exported on '
'connection %r' % (self, self._connection))
if (self._object_path is not None and
not self.SUPPORTS_MULTIPLE_OBJECT_PATHS and
self._object_path != path):
raise ValueError('%r is already exported at object '
'path %s' % (self, self._object_path))
connection._register_object_path(path, self._message_cb,
self._unregister_cb,
self._fallback)
if self._connection is None:
self._connection = connection
elif self._connection is not connection:
self._connection = _MANY
if self._object_path is None:
self._object_path = path
elif self._object_path != path:
self._object_path = _MANY
self._locations.append((connection, path, self._fallback))
finally:
self._locations_lock.release()
def remove_from_connection(self, connection=None, path=None):
"""Make this object inaccessible via the given D-Bus connection
and object path. If no connection or path is specified,
the object ceases to be accessible via any connection or path.
:Parameters:
`connection` : dbus.connection.Connection or None
Only remove the object from this Connection. If None,
remove from all Connections on which it's exported.
`path` : dbus.ObjectPath or other str, or None
Only remove the object from this object path. If None,
remove from all object paths.
:Raises LookupError:
if the object was not exported on the requested connection
or path, or (if both are None) was not exported at all.
:Since: 0.81.1
"""
self._locations_lock.acquire()
try:
if self._object_path is None or self._connection is None:
raise LookupError('%r is not exported' % self)
if connection is not None or path is not None:
dropped = []
for location in self._locations:
if ((connection is None or location[0] is connection) and
(path is None or location[1] == path)):
dropped.append(location)
else:
dropped = self._locations
self._locations = []
if not dropped:
raise LookupError('%r is not exported at a location matching '
'(%r,%r)' % (self, connection, path))
for location in dropped:
try:
location[0]._unregister_object_path(location[1])
except LookupError:
pass
if self._locations:
try:
self._locations.remove(location)
except ValueError:
pass
finally:
self._locations_lock.release()
def _unregister_cb(self, connection):
# there's not really enough information to do anything useful here
_logger.info('Unregistering exported object %r from some path '
'on %r', self, connection)
def _message_cb(self, connection, message):
if not isinstance(message, MethodCallMessage):
return
try:
# lookup candidate method and parent method
method_name = message.get_member()
interface_name = message.get_interface()
(candidate_method, parent_method) = _method_lookup(self, method_name, interface_name)
# set up method call parameters
args = message.get_args_list(**parent_method._dbus_get_args_options)
keywords = {}
if parent_method._dbus_out_signature is not None:
signature = Signature(parent_method._dbus_out_signature)
else:
signature = None
# set up async callback functions
if parent_method._dbus_async_callbacks:
(return_callback, error_callback) = parent_method._dbus_async_callbacks
keywords[return_callback] = lambda *retval: _method_reply_return(connection, message, method_name, signature, *retval)
keywords[error_callback] = lambda exception: _method_reply_error(connection, message, exception)
# include the sender etc. if desired
if parent_method._dbus_sender_keyword:
keywords[parent_method._dbus_sender_keyword] = message.get_sender()
if parent_method._dbus_path_keyword:
keywords[parent_method._dbus_path_keyword] = message.get_path()
if parent_method._dbus_rel_path_keyword:
path = message.get_path()
rel_path = path
for exp in self._locations:
# pathological case: if we're exported in two places,
# one of which is a subtree of the other, then pick the
# subtree by preference (i.e. minimize the length of
# rel_path)
if exp[0] is connection:
if path == exp[1]:
rel_path = '/'
break
if exp[1] == '/':
# we already have rel_path == path at the beginning
continue
if path.startswith(exp[1] + '/'):
# yes we're in this exported subtree
suffix = path[len(exp[1]):]
if len(suffix) < len(rel_path):
rel_path = suffix
rel_path = ObjectPath(rel_path)
keywords[parent_method._dbus_rel_path_keyword] = rel_path
if parent_method._dbus_destination_keyword:
keywords[parent_method._dbus_destination_keyword] = message.get_destination()
if parent_method._dbus_message_keyword:
keywords[parent_method._dbus_message_keyword] = message
if parent_method._dbus_connection_keyword:
keywords[parent_method._dbus_connection_keyword] = connection
# call method
retval = candidate_method(self, *args, **keywords)
# we're done - the method has got callback functions to reply with
if parent_method._dbus_async_callbacks:
return
# otherwise we send the return values in a reply. if we have a
# signature, use it to turn the return value into a tuple as
# appropriate
if signature is not None:
signature_tuple = tuple(signature)
# if we have zero or one return values we want make a tuple
# for the _method_reply_return function, otherwise we need
# to check we're passing it a sequence
if len(signature_tuple) == 0:
if retval == None:
retval = ()
else:
raise TypeError('%s has an empty output signature but did not return None' %
method_name)
elif len(signature_tuple) == 1:
retval = (retval,)
else:
if isinstance(retval, Sequence):
# multi-value signature, multi-value return... proceed
# unchanged
pass
else:
raise TypeError('%s has multiple output values in signature %s but did not return a sequence' %
(method_name, signature))
# no signature, so just turn the return into a tuple and send it as normal
else:
if retval is None:
retval = ()
elif (isinstance(retval, tuple)
and not isinstance(retval, Struct)):
# If the return is a tuple that is not a Struct, we use it
# as-is on the assumption that there are multiple return
# values - this is the usual Python idiom. (fd.o #10174)
pass
else:
retval = (retval,)
_method_reply_return(connection, message, method_name, signature, *retval)
except Exception as exception:
# send error reply
_method_reply_error(connection, message, exception)
@method(INTROSPECTABLE_IFACE, in_signature='', out_signature='s',
path_keyword='object_path', connection_keyword='connection')
def Introspect(self, object_path, connection):
"""Return a string of XML encoding this object's supported interfaces,
methods and signals.
"""
reflection_data = _dbus_bindings.DBUS_INTROSPECT_1_0_XML_DOCTYPE_DECL_NODE
reflection_data += '<node name="%s">\n' % object_path
interfaces = self._dbus_class_table[self.__class__.__module__ + '.' + self.__class__.__name__]
for (name, funcs) in interfaces.items():
reflection_data += ' <interface name="%s">\n' % (name)
for func in funcs.values():
if getattr(func, '_dbus_is_method', False):
reflection_data += self.__class__._reflect_on_method(func)
elif getattr(func, '_dbus_is_signal', False):
reflection_data += self.__class__._reflect_on_signal(func)
reflection_data += ' </interface>\n'
for name in connection.list_exported_child_objects(object_path):
reflection_data += ' <node name="%s"/>\n' % name
reflection_data += '</node>\n'
return reflection_data
def __repr__(self):
where = ''
if (self._object_path is not _MANY
and self._object_path is not None):
where = ' at %s' % self._object_path
return '<%s.%s%s at %#x>' % (self.__class__.__module__,
self.__class__.__name__, where,
id(self))
__str__ = __repr__
class FallbackObject(Object):
"""An object that implements an entire subtree of the object-path
tree.
:Since: 0.82.0
"""
SUPPORTS_MULTIPLE_OBJECT_PATHS = True
def __init__(self, conn=None, object_path=None):
"""Constructor.
Note that the superclass' ``bus_name`` __init__ argument is not
supported here.
:Parameters:
`conn` : dbus.connection.Connection or None
The connection on which to export this object. If this is not
None, an `object_path` must also be provided.
If None, the object is not initially available on any
Connection.
`object_path` : str or None
A D-Bus object path at which to make this Object available
immediately. If this is not None, a `conn` must also be
provided.
This object will implements all object-paths in the subtree
starting at this object-path, except where a more specific
object has been added.
"""
super(FallbackObject, self).__init__()
self._fallback = True
if conn is None:
if object_path is not None:
raise TypeError('If object_path is given, conn is required')
elif object_path is None:
raise TypeError('If conn is given, object_path is required')
else:
self.add_to_connection(conn, object_path)