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| -rw-r--r-- | ChangeLog | 5 | ||||
| -rw-r--r-- | doc/dbus-tutorial.xml | 548 |
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@@ -1,3 +1,8 @@ +2006-01-25 Simon McVittie <simon.mcvittie@collabora.co.uk> + + * doc/dbus-tutorial.xml: Replace Python section of tutorial with + a pointer to the tutorial maintained as part of dbus-python + 2006-12-31 Ralf Habacker <ralf.habacker@freenet.de> * dbus/dbus-sysdeps-unix.c: unix compile fix, moved diff --git a/doc/dbus-tutorial.xml b/doc/dbus-tutorial.xml index add59e1a..5c385f0e 100644 --- a/doc/dbus-tutorial.xml +++ b/doc/dbus-tutorial.xml @@ -1640,551 +1640,13 @@ my_object_increment_retval_error (MyObject *obj, gint32 x, GError **error) </sect1> <sect1 id="python-client"> - <title>Python API: Using Remote Objects</title> + <title>Python API</title> <para> - The Python bindings provide a simple to use interface for talking over D-Bus. - Where possible much of the inner-workings of D-Bus are hidden behind what looks - like normal Python objects. + The Python API, dbus-python, is now documented separately in + <ulink url="http://dbus.freedesktop.org/doc/dbus-python/doc/tutorial.html">the dbus-python tutorial</ulink> (also available in doc/tutorial.txt, + and doc/tutorial.html if built with python-docutils, in the dbus-python + source distribution). </para> - <sect2 id="python-typemappings"> - <title>D-Bus - Python type mappings</title> - <para> - While python itself is a largely untyped language D-Bus provides a simple type system - for talking with other languages which may be strongly typed. Python for the most part - tries automatically map python objects to types on the bus. It is none the less good to - know what the type mappings are so one can better utilize services over the bus. - </para> - <sect3 id="python-basic-typemappings"> - <title>Basic type mappings</title> - <para> - Below is a list of the basic types, along with their associated - mapping to a Python object. - <informaltable> - <tgroup cols="3"> - <thead> - <row> - <entry>D-Bus basic type</entry> - <entry>Python wrapper</entry> - <entry>Notes</entry> - </row> - </thead> - <tbody> - <row> - <entry><literal>BYTE</literal></entry> - <entry><literal>dbus.Byte</literal></entry> - <entry></entry> - </row><row> - <entry><literal>BOOLEAN</literal></entry> - <entry><literal>dbus.Boolean</literal></entry> - <entry>Any variable assigned a True or False boolean value will automatically be converted into a BOOLEAN over the bus</entry> - </row><row> - <entry><literal>INT16</literal></entry> - <entry><literal>dbus.Int16</literal></entry> - <entry></entry> - </row><row> - <entry><literal>UINT16</literal></entry> - <entry><literal>dbus.UInt16</literal></entry> - <entry></entry> - </row><row> - <entry><literal>INT32</literal></entry> - <entry><literal>dbus.Int32</literal></entry> - <entry>This is the default mapping for Python integers</entry> - </row><row> - <entry><literal>UINT32</literal></entry> - <entry><literal>dbus.UInt32</literal></entry> - <entry></entry> - </row><row> - <entry><literal>INT64</literal></entry> - <entry><literal>dbus.Int64</literal></entry> - <entry></entry> - </row><row> - <entry><literal>UINT64</literal></entry> - <entry><literal>dbus.UInt64</literal></entry> - <entry></entry> - </row><row> - <entry><literal>DOUBLE</literal></entry> - <entry><literal>dbus.Double</literal></entry> - <entry>Any variable assigned a floating point number will automatically be converted into a DOUBLE over the bus</entry> - </row><row> - <entry><literal>STRING</literal></entry> - <entry><literal>dbus.String</literal></entry> - <entry>Any variable assigned a quoted string will automatically be converted into a STRING over the bus</entry> - </row><row> - <entry><literal>OBJECT_PATH</literal></entry> - <entry><literal>dbus.ObjectPath</literal></entry> - <entry></entry> - </row> - </tbody> - </tgroup> - </informaltable> - </para> - </sect3> - <sect3 id="python-container-typemappings"> - <title>Container type mappings</title> - <para> - The D-Bus type system also has a number of "container" - types, such as <literal>DBUS_TYPE_ARRAY</literal> and - <literal>DBUS_TYPE_STRUCT</literal>. The D-Bus type system - is fully recursive, so one can for example have an array of - array of strings (i.e. type signature - <literal>aas</literal>). - </para> - <para> - D-Bus container types have native corresponding built-in Python types - so it is easy to use them. - <informaltable> - <tgroup cols="3"> - <thead> - <row> - <entry>D-Bus type</entry> - <entry>Python type</entry> - <entry>Python wrapper</entry> - <entry>Notes</entry> - </row> - </thead> - <tbody> - <row> - <entry><literal>ARRAY</literal></entry> - <entry><literal>Python lists</literal></entry> - <entry><literal>dbus.Array</literal></entry> - <entry>Python lists, denoted by square brackets [], are converted into arrays and visa versa. - The one restriction is that when sending a Python list each element of the list must be of the same - type. This is because D-Bus arrays can contain only one element type. Use Python tuples for mixed types. - - When using the wrapper you may also specify a type or signature of the elements contained in the Array. - This is manditory when passing an empty Array to a method on the bus because Python can not guess at the - contents of an empty array. For example if a method is expecting an Array of int32's and you need to pass - it an empty Array you would do it as such: - - <programlisting>emptyint32array = dbus.Array([], type=dbus.Int32)</programlisting> - - or - - <programlisting>emptyint32array = dbus.Array([], signature="i")</programlisting> - - Note that dbus.Array derives from list so it acts just like a python list. - </entry> - </row> - <row> - <entry><literal>STRUCT</literal></entry> - <entry><literal>Python tuple</literal></entry> - <entry><literal>dbus.Struct</literal></entry> - <entry>Python tuples, denoted by parentheses (,), are converted into structs and visa versa. - Tuples can have mixed types.</entry> - </row> - <row> - <entry><literal>DICTIONARY</literal></entry> - <entry><literal>Python dictionary</literal></entry> - <entry><literal>dbus.Dictionary</literal></entry> - <entry>D-Bus doesn't have an explicit dictionary type. Instead it uses LISTS of DICT_ENTRIES to - represent a dictionary. A DICT_ENTRY is simply a two element struct containing a key/value pair. - Python dictionaries are automatically converted to a LIST of DICT_ENTRIES and visa versa. - - Since dictonaries are described as lists of dict_entries we also need the signature in order - to pass empty dictionaries. The wrapper provides a way of specifying this through the key_type/value_type - type parameters or the signature parameters. To send an empty Dictionary where the key is a string - and the value is a string you would do it as such: - - <programlisting>emptystringstringdict = dbus.Dictionary({}, key_type=dbus.String, value_type=dbus.Value)</programlisting> - - or - - <programlisting>emptystringstringdict = dbus.Dictionary({}, signature="ss")</programlisting> - - Note that dbus.Dictionary derives from dict so it acts just like a python dictionary. - </entry> - </row> - <row> - <entry><literal>VARIANT</literal></entry> - <entry><literal>any type</literal></entry> - <entry><literal>dbus.Variant</literal></entry> - <entry>A variant is a container for any type. Python exports its methods to accept only variants - since we are an untyped language and can demarshal into any Python type. - - To send a variant you must first wrap it in a<literal>dbus.Variant</literal>. If no type or signiture is - given to the variant the marshaler will get the type from the contents.</entry> - </row> - - </tbody> - </tgroup> - </informaltable> - </para> - </sect3> - </sect2> - <sect2 id="python-invoking-methods"> - <title>Invoking Methods</title> - <para>Here is a D-Bus program using the Python bindings to get a listing of all names on the session bus. -<programlisting> -import dbus - -bus = dbus.SessionBus() -proxy_obj = bus.bus.get_object('org.freedesktop.DBus', '/org/freedesktop/DBus') -dbus_iface = dbus.Interface(proxy_obj, 'org.freedesktop.DBus') - -print dbus_iface.ListNames() -</programlisting> - </para> - <para> - Notice I get an interface on the proxy object and use that to make the call. While the specifications - state that you do not need to specify an interface if the call is unambiguous (i.e. only one method implements - that name) due to a bug on the bus that drops messages which don't have an interface field you need to specify - interfaces at this time. In any event it is always good practice to specify the interface of the method you - wish to call to avoid any side effects should a method of the same name be implemented on another interface. - </para> - <para> - You can specify the interface for a single call using the dbus_interface keyword. -<programlisting> -proxy_obj.ListNames(dbus_interface = 'org.freedesktop.DBus') -</programlisting> - </para> - <para> - This is all fine and good if all you want to do is call methods on the bus and then exit. In order to - do more complex things such as use a GUI or make asynchronous calls you will need a mainloop. You would use - asynchronous calls because in GUI applications it is very bad to block for any long period of time. This cause - the GUI to seem to freeze. Since replies to D-Bus messages can take an indeterminate amount of time using async - calls allows you to return control to the GUI while you wait for the reply. This is exceedingly easy to do in - Python. Here is an example using the GLib/GTK+ mainloop. -<programlisting> -import gobject -import dbus -if getattr(dbus, 'version', (0,0,0)) >= (0,41,0): - import dbus.glib - -def print_list_names_reply(list): - print str(list) - -def print_error(e): - print str(e) - -bus = dbus.SessionBus() -proxy_obj = bus.bus.get_object('org.freedesktop.DBus', '/org/freedesktop/DBus') -dbus_iface = dbus.Interface(proxy_obj, 'org.freedesktop.DBus') - -dbus_iface.ListNames(reply_handler=print_list_names_reply, error_handler=print_error) - -mainloop = gobject.MainLoop() -mainloop.run() -</programlisting> - </para> - <para> - In the above listing you will notice the reply_handler and error_handler keywords. These tell the method that - it should be called async and to call print_list_names_reply or print_error depending if you get a reply or an error. - The signature for replys depends on the number of arguments being sent back. Error handlers always take one parameter - which is the error object returned. - </para> - <para> - You will also notice that I check the version of the dbus bindings before importing dbus.glib. In older versions - glib was the only available mainloop. As of version 0.41.0 we split out the glib dependency to allow for other mainloops - to be implemented. Notice also the python binding version does not match up with the D-Bus version. Once we reach 1.0 - this should change with Python changes simply tracking the D-Bus changes. - While the glib mainloop is the only mainloop currently implemented, integrating other mainloops should - be very easy to do. There are plans for creating a a generic mainloop to be the default for non gui programs. - </para> - </sect2> - <sect2 id="python-listening-for-signals"> - <title>Listening for Signals</title> - <para> - Signals are emitted by objects on the bus to notify listening programs that an event has occurred. There are a couple of ways - to register a signal handler on the bus. One way is to attach to an already created proxy using the connect_to_signal method - which takes a signal name and handler as arguments. Let us look at an example of connecting to the HAL service to receive - signals when devices are added and removed and when devices register a capability. This example assumes you have HAL already running. -<programlisting> -import gobject -import dbus -if getattr(dbus, 'version', (0,0,0)) >= (0,41,0): - import dbus.glib - -def device_added_callback(udi): - print 'Device with udi %s was added' % (udi) - -def device_removed_callback(udi): - print 'Device with udi %s was added' % (udi) - -def device_capability_callback(udi, capability): - print 'Device with udi %s added capability %s' % (udi, capability) - -bus = dbus.SystemBus() -hal_manager_obj = bus.get_object('org.freedesktop.Hal', - '/org/freedesktop/Hal/Manager') -hal_manager = dbus.Interface(hal_manager_obj, - 'org.freedesktop.Hal.Manager') - -hal_manager.connect_to_signal('DeviceAdded', device_added_callback) -hal_manager.connect_to_signal('DeviceRemoved', device_removed_callback) -hal_manager.connect_to_signal('NewCapability', device_capability_callback) - -mainloop = gobject.MainLoop() -mainloop.run() -</programlisting> - </para> - <para> - The drawback of using this method is that the service that you are connecting to has to be around when you register - your signal handler. While HAL is guaranteed to be around on systems that use it this is not always the case for every - service on the bus. Say our program started up before HAL, we could connect to the signal by adding a signal receiver - directly to the bus. -<programlisting> -bus.add_signal_receiver(device_added_callback, - 'DeviceAdded', - 'org.freedesktop.Hal.Manager', - 'org.freedesktop.Hal', - '/org/freedesktop/Hal/Manager') - -bus.add_signal_receiver(device_removed_callback, - 'DeviceRemoved', - 'org.freedesktop.Hal.Manager', - 'org.freedesktop.Hal', - '/org/freedesktop/Hal/Manager') - -bus.add_signal_receiver(device_capability_callback, - 'DeviceAdded', - 'org.freedesktop.Hal.Manager', - 'org.freedesktop.Hal', - '/org/freedesktop/Hal/Manager') -</programlisting> - </para> - <para> - All this can be done without creating the proxy object if one wanted to but in most cases you would want to have - a reference to the object so once a signal was received operations could be executed on the object. - </para> - <sidebar> - <title>Signal matching on arguments</title> - <para> - Starting with D-Bus 0.36 and the (0, 43, 0) version of the python - bindings you can now add a match on arguments being sent in a signal. - This is useful for instance for only getting NameOwnerChanged - signals for your service. Lets say we create a name on the bus called - 'org.foo.MyName' we could also add a match to just get - NameOwnerChanges for that name as such: -<programlisting> -bus.add_signal_receiver(myname_changed, - 'NameOwnerChanged', - 'org.freedesktop.DBus', - 'org.freedesktop.DBus', - '/org/freedesktop/DBus', - arg0='org.foo.MyName') -</programlisting> - - It is as simple as that. To match the second arg you would use arg1=, - the third arg2=, etc. - </para> - </sidebar> - <sidebar> - <title>Cost of Creating a Proxy Object</title> - <para> - Note that creating proxy objects can have an associated processing cost. When introspection is implemented - a proxy may wait for introspection data before processing any requests. It is generally good practice to - create proxies once and reuse the proxy when calling into the object. Constantly creating the same proxy - over and over again can become a bottleneck for your program. - </para> - </sidebar> - <para> - TODO: example of getting information about devices from HAL - </para> - </sect2> - </sect1> - - <sect1 id="python-server"> - <title>Python API: Implementing Objects</title> - <para> - Implementing object on the bus is just as easy as invoking methods or listening for signals on the bus. - </para> - <sidebar> - <title>Version Alert</title> - <para> - The Python D-Bus bindings require version 2.4 or greater of Python when creating D-Bus objects. - </para> - </sidebar> - - <sect2 id="python-inheriting-from-dbus-object"> - <title>Inheriting From dbus.service.Object</title> - <para> - In order to export a Python object over the bus one must first get a bus name and then create - a Python object that inherits from dbus.service.Object. The following is the start of an example - HelloWorld object that we want to export over the session bus. -<programlisting> -import gobject -import dbus -import dbus.service -if getattr(dbus, 'version', (0,0,0)) >= (0,41,0): - import dbus.glib - -class HelloWorldObject(dbus.service.Object): - def __init__(self, bus_name, object_path='/org/freedesktop/HelloWorldObject'): - dbus.service.Object.__init__(self, bus_name, object_path) - -session_bus = dbus.SessionBus() -bus_name = dbus.service.BusName('org.freedesktop.HelloWorld', bus=session_bus) -object = HelloWorldObject(bus_name) - -mainloop = gobject.MainLoop() -mainloop.run() -</programlisting> - </para> - <para> - Here we got the session bus, then created a BusName object which requests a name on the bus. - We pass that bus name to the HelloWorldObject object which inherits from dbus.service.Object. - We now have an object on the bus but it is pretty useless. - </para> - </sect2> - <sect2 id="python-exporting-methods"> - <title>Exporting Methods Over The Bus</title> - <para> - Let's make this object do something and export a method over the bus. -<programlisting> -import gobject -import dbus -import dbus.service -if getattr(dbus, 'version', (0,0,0)) >= (0,41,0): - import dbus.glib - -class HelloWorldObject(dbus.service.Object): - def __init__(self, bus_name, object_path='/org/freedesktop/HelloWorldObject'): - dbus.service.Object.__init__(self, bus_name, object_path) - - @dbus.service.method('org.freedesktop.HelloWorldIFace') - def hello(self): - return 'Hello from the HelloWorldObject' - -session_bus = dbus.SessionBus() -bus_name = dbus.service.BusName('org.freedesktop.HelloWorld', bus=session_bus) -object = HelloWorldObject(bus_name) - -mainloop = gobject.MainLoop() -mainloop.run() -</programlisting> - </para> - <sidebar> - <title>Python Decorators</title> - <para> - Notice the @ symbol on the line before the hello method. This is a new directive introduced in - Python 2.4. It is called a decorator and it "decorates" methods. All you have to know is that - it provides metadata that can then be used to alter the behavior of the method being decorated. - In this case we are telling the bindings that the hello method should be exported as a D-Bus method - over the bus. - </para> - </sidebar> - <para> - As you can see we exported the hello method as part of the org.freedesktop.HelloWorldIFace interface. - It takes no arguments and returns a string to the calling program. Let's create a proxy and invoke this - method. -<programlisting> -import dbus - -bus = dbus.SessionBus() -proxy_obj = bus.bus.get_object('org.freedesktop.HelloWorld', '/org/freedesktop/HelloWorldObject') -iface = dbus.Interface(proxy_obj, 'org.freedesktop.HelloWorldIFace') - -print iface.hello() -</programlisting> - </para> - <para> - When invoking methods exported over the bus the bindings automatically know how many parameters - the method exports. You can even make a method that exports an arbitrary number of parameters. - Also, whatever you return will automatically be transfered as a reply over the bus. Some examples. -<programlisting> - @dbus.service.method('org.freedesktop.HelloWorldIFace') - def one_arg(self, first_arg): - return 'I got arg %s' % first_arg - - @dbus.service.method('org.freedesktop.HelloWorldIFace') - def two_args(self, first_arg, second_arg): - return ('I got 2 args', first_arg, second_arg) - - @dbus.service.method('org.freedesktop.HelloWorldIFace') - def return_list(self): - return [1, 2, 3, 4, 5, 6] - - @dbus.service.method('org.freedesktop.HelloWorldIFace') - def return_dict(self): - return {one: '1ne', two: '2wo', three: '3ree'} -</programlisting> - </para> - </sect2> - <sect2 id="python-emitting-signals"> - <title>Emitting Signals</title> - <para> - Setting up signals to emit is just as easy as exporting methods. It uses the same syntax as methods. -<programlisting> -import gobject -import dbus -import dbus.service -if getattr(dbus, 'version', (0,0,0)) >= (0,41,0): - import dbus.glib - -class HelloWorldObject(dbus.service.Object): - def __init__(self, bus_name, object_path='/org/freedesktop/HelloWorldObject'): - dbus.service.Object.__init__(self, bus_name, object_path) - - @dbus.service.method('org.freedesktop.HelloWorldIFace') - def hello(self): - return 'Hello from the HelloWorldObject' - - @dbus.service.signal('org.freedesktop.HelloWorldIFace') - def hello_signal(self, message): - pass - -session_bus = dbus.SessionBus() -bus_name = dbus.service.BusName('org.freedesktop.HelloWorld', bus=session_bus) -object = HelloWorldObject(bus_name) - -object.hello_signal('I sent a hello signal') - -mainloop = gobject.MainLoop() -mainloop.run() -</programlisting> - </para> - <para> - Adding a @dbus.service.signal decorator to a method turns it into a signal emitter. You can put code - in this method to do things like keep track of how many times you call the emitter or to print out debug - messages but for the most part a pass noop will do. Whenever you call the emitter a signal will be emitted - with the parameters you passed in as arguments. In the above example we send the message 'I sent a hello signal' - with the signal. - </para> - </sect2> - <sect2 id="python-inheriting-and-overriding"> - <title>Inheriting from HelloWorldObject</title> - <para> - One of the cool things you can do in Python is inherit from another D-Bus object. We use this trick in - the bindings to provide a default implementation for the org.freedesktop.DBus.Introspectable interface. - Let's inherit from the HelloWorldObject example above and overide the hello method to say goodbye. -<programlisting> -class HelloWorldGoodbyeObject(HelloWorldObject): - def __init__(self, bus_name, object_path='/org/freedesktop/HelloWorldGoodbyeObject'): - HelloWorldObject.__init__(self, bus_name, object_path) - - @dbus.service.method('org.freedesktop.HelloWorldGoodbyeIFace') - def hello(self): - return 'Goodbye' - -goodbye_object = HelloWorldGoodbyeObject(bus_name) -</programlisting> - </para> - <para> - Let's now call both methods with a little help from interfaces. -<programlisting> -import dbus - -bus = dbus.SessionBus() -proxy_obj = bus.bus.get_object('org.freedesktop.HelloWorld', '/org/freedesktop/HelloWorldGoodbyeObject') - -print proxy_obj.hello(dbus_interface='org.freedesktop.HelloWorldIFace') -print proxy_obj.hello(dbus_interface='org.freedesktop.HelloWorldGoodbyeIFace') -</programlisting> - </para> - <para> - This should print out 'Hello from the HelloWorldObject' followed by a 'Goodbye'. - </para> - </sect2> - <sect2 id="python-conclusion"> - <title>Conclusion</title> - <para> - As you can see, using D-Bus from Python is an extremely easy proposition. Hopefully - the tutorial has been helpful in getting you started. If you need anymore help please - feel free to post on the <ulink url="http://lists.freedesktop.org/mailman/listinfo/dbus/">mailing list</ulink>. - The Python bindings are still in a state of flux and there may be API changes in the future. - This tutorial will be updated if such changes occur. - </para> - </sect2> </sect1> <sect1 id="qt-client"> |