examples: add helloworld example

Add a straight 1:1 copy from cores' helloworld.c to show how the c api maps into
the pythong bindings. It would rock to have the same in other bindings.

examples/Makefile.am

@@ -10,6 +10,7 @@ examples_DATA = 	\
 	fvumeter.py	\
 	gst-discover	\
 	gstfile.py	\
+	helloworld.py	\
 	mixer.py	\
 	play.py		\
 	pipeline-tester \

examples/helloworld.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python
+
+import sys
+
+import gobject
+gobject.threads_init()
+
+import pygst
+pygst.require('0.10')
+import gst
+
+def bus_call(bus, message, loop):
+    t = message.type
+    if t == gst.MESSAGE_EOS:
+        sys.stout.write("End-of-stream\n")
+        loop.quit()
+    elif t == gst.MESSAGE_ERROR:
+        err, debug = message.parse_error()
+        sys.stderr.write("Error: %s: %s\n" % err, debug)
+        loop.quit()
+    return True
+
+def main(args):
+    if len(args) != 2:
+        sys.stderr.write("usage: %s <media file or uri>\n" % args[0])
+        sys.exit(1)
+        
+    playbin = gst.element_factory_make("playbin2", None)
+    if not playbin:
+        sys.stderr.write("'playbin2' gstreamer plugin missing\n")
+        sys.exit(1)
+
+    # take the commandline argument and ensure that it is a uri
+    if gst.uri_is_valid(args[1]):
+      uri = args[1]
+    else:
+      uri = gst.filename_to_uri(args[1])
+    playbin.set_property('uri', uri)
+
+    # create and event loop and feed gstreamer bus mesages to it
+    loop = gobject.MainLoop()
+
+    bus = playbin.get_bus()
+    bus.add_watch(bus_call, loop)
+    
+    # start play back and listed to events
+    playbin.set_state(gst.STATE_PLAYING)
+    loop.run()
+    
+    # cleanup
+    playbin.set_state(gst.STATE_NULL)
+
+if __name__ == '__main__':
+    sys.exit(main(sys.argv))