API changes in dbus-python 0.80

Author

Simon McVittie

Contact

simon.mcvittie@collabora.co.uk

Organization

Collabora Ltd

Date

2006-11-23

Type changes

• The Byte constructor accepts either single-byte strings, or integers in the range 0 to 255.

• There is no Variant type any more. Instead, the variant_level attribute on D-Bus types gives the number of variant wrappers in which it is contained; this is to remove ambiguity. For instance, calling this method:

  @dbus.service.method('com.example', in_signature='v', out_signature='')
  def Print(self, variant):
      print repr(variant)
  

  yields the following results:

  # on the wire: Variant containing Int32
  Int32(0, variant_level=1)
  # on the wire: Variant containing Variant containing Int32
  Int32(0, variant_level=2)
  

  Once an object of a D-Bus type has been constructed, its variant_level cannot be altered.

• The D-Bus integer types (dbus.Int32, etc.) are properly range-checked.

• The Array constructor takes arguments (iterable[, signature]) rather than (iterable[, type][, signature]); ditto for Dict.

Calling conventions

• In method parameters, method returns from proxy methods, etc., integers arrive as instances of dbus.Int32 etc., bytes arrive as Byte, and so on, rather than everything being converted to an appropriate built-in Python type. This means you can tell exactly what arguments went over the bus, and their types.

• Proxy methods with multiple return values return a tuple rather than a list.

• Calling a proxy method with reply ignored, or with async handlers, returns None

dbus_bindings

• ConnectionError no longer exists (it was never raised)

• dbus_bindings is now called _dbus_bindings, and is considerably different internally:

  • connections are private at the libdbus level: shared connections are only shared among Python code

  • The MessageIter stuff is now done in C: there’s a much simpler Python API, Message.append(...) where positional arguments are the things to be appended, and the keyword argument signature controls how objects are interpreted

  • The signature-guessing algorithm used if there is no proper signature is exposed as a static method, Message.guess_signature(*args)

  • Bus is a subclass of Connection rather than being a wrapper object which has-a Connection

  • The timeouts in _send_with_reply and in _send_with_reply_and_block are in (possibly fractional) seconds, as is conventional in Python

  • The specialized Message subclasses have names ending with Message

• There is a small amount of compatibility glue in a new dbus_bindings module (also dbus.dbus_bindings) which should enable most current code to work - this is deprecated, and will disappear in a future version of dbus-python

Main loops

Main loop handling is different - instead of the use_default_mainloop keyword argument to Bus and subclasses, there’s now mainloop which takes an instance of dbus.mainloop.NativeMainLoop.

Alternatively, you can set a default main loop by calling dbus.set_default_main_loop() and passing it a NativeMainLoop, or by passing set_as_default=True to the factory function from which you obtained the native main loop.

The plan is that in a future version of dbus-python there will be an abstract base class dbus.mainloop.MainLoop (or something); when it’s added, instances of its subclasses will be accepted wherever a NativeMainLoop instance is now. This will let you wrap main loops using a Python API. This will be used to implement SimpleMainLoop (a pure-Python main loop which can only do D-Bus) and a Twisted main-loop wrapper.

The only working mainloop implementation is (still) GLib; you can get a NativeMainLoop instance by:

from dbus.mainloop.glib import DBusGMainLoop
my_native_main_loop = DBusGMainLoop(set_as_default=True)

The above is how the highly magical dbus.glib module is now implemented. At some point dbus.glib will be deprecated, since it’s non-obvious, and pychecker will usually complain if you use it correctly!

At the moment the GLib main loop always uses the default main context; python-gobject will probably need to add some extra API before we can allow other main-contexts to be used.