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General Information

.. py:currentmodule:: sdbus

Blocking vs Async

Python-sdbus supports both blocking and async IO.

Regular python functions are always blocking.

Asyncio is a part of python standard library that allows non-blocking io.

Asyncio documentation

Generally blocking IO should only be used for simple scripts and programs that interact with existing D-Bus objects.

Blocking:

  • Blocking is easier to initiate (no event loop)
  • Properties behave exactly as Python properties do. (i.e. can assign with '=' operator)
  • Only allows one request at a time.
  • No D-Bus signals.
  • Cannot serve objects, only interact with existing object on D-Bus.

:doc:`/sync_quick`

:doc:`/sync_api`

Asyncio:

  • Calls need to be await ed.
  • Multiple requests at the same time.
  • Serve object on D-Bus for other programs.
  • D-Bus Signals.

:doc:`/asyncio_quick`

:doc:`/asyncio_api`

D-Bus types conversion

D-Bus types reference

Note

Python integers are unlimited size but D-Bus integers are not. All integer types raise :py:exc:`OverflowError` if you try to pass number outside the type size.

Unsigned integers range is 0 < (2**bit_size)-1.

Signed integers range is -(2**(bit_size-1)) < (2**(bit_size-1))-1.

Name D-Bus type Python type Description
Boolean b :py:obj:`bool` :py:obj:`True` or :py:obj:`False`
Byte y :py:obj:`int` Unsigned 8-bit integer. Note: array of bytes (ay) has different type in python domain.
Int16 n :py:obj:`int` Signed 16-bit integer.
Uint16 q :py:obj:`int` Unsigned 16-bit integer.
Int32 i :py:obj:`int` Signed 32-bit integer.
Uint32 u :py:obj:`int` Unsigned 32-bit integer.
Int64 x :py:obj:`int` Signed 64-bit integer.
Uint64 t :py:obj:`int` Unsigned 64-bit integer.
Double d :py:obj:`float` Float point number
Unix FD h :py:obj:`int` File descriptor
String s :py:obj:`str` String
Object Path o :py:obj:`str` Syntactically correct D-Bus object path
Signature g :py:obj:`str` D-Bus type signature
Array a :py:obj:`list`

List of some single type.

Example: as array of strings
Byte Array ay :py:obj:`bytes` Array of bytes. Not a unique type in D-Bus but a different type in Python. Accepts both :py:obj:`bytes` and :py:obj:`bytearray`. Used for binary data.
Struct () :py:obj:`tuple`

Tuple.

Example: (isax) tuple of int, string and array of int.
Dictionary a{} :py:obj:`dict`

Dictionary with key type and value type.

Note: Dictionary is always a part of array. I.E. a{si} is the dict with string keys and integer values. {si} is NOT a valid signature.
Variant v :py:obj:`tuple`

Unknown type that can be any single type. In Python represented by a tuple of a signature string and a single type.

Example: ("s", "test") variant of a single string

Name conversions

D-Bus uses CamelCase for method names.

Python uses snake_case.

When decorating a method name will be automatically translated from snake_case to CamelCase. Example: close_notification -> CloseNotification

However, all decorators have a parameter to force D-Bus name to a specific value. See API documentation for a particular decorator.

Default bus

Most object methods that take a bus as a parameter will use a thread-local default bus connection if a bus object is not explicitly passed.

Session bus is default bus when running as a user and system bus otherwise.

The :py:func:`request_default_bus_name_async <sdbus.default_bus.request_default_bus_name_async>` and :py:func:`request_default_bus_name <sdbus.default_bus.request_default_bus_name>` can be used to acquire a service name on the default bus.

Use :py:func:`sd_bus_open_user` and :py:func:`sd_bus_open_system` to acquire a specific bus connection.

The :py:func:`set_default_bus <sdbus.default_bus.set_default_bus>` can be used to set the new thread-local bus. This should be done before any objects that take bus as an init argument are created. If no bus has been set the new bus will be initialized and set as thread-local default.

The bus can also be set as default for the current context using :py:func:`set_context_default_bus <sdbus.default_bus.set_context_default_bus>`. The context refers to the standard library's contextvars module context variables frequently used in asyncio frameworks. Context-local default bus has higher priority over thread-local default bus.

Glossary

  • Bus object representing connection to D-Bus.
  • Proxy Python object that represents an object on D-Bus.
    Without proxy you manipulate messages directly.
  • Remote something that exists outside current Python process.
  • Local something that exists inside current Python scope.
  • Service Name a well known name that an process can acquire on D-Bus.
    For example, systemd acquires org.freedesktop.systemd1 name.
  • Signature D-Bus type definition. Represented by a string. See :ref:`dbus-types`.

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