[API add] Add Signal class for adding and connecting custom signals.

The Signal class provides easy creation of signals and removes the
need for __gsignals__ in client code. The Signal class can also be
used as a decorator for wrapping up the custom closure. As well as
providing a "BoundSignal" when accessed on an instance for making
connections without specifying a signal name string.
Python3 annotations can also be used to supply closure argument and
return types when Signal is used as a decorator. For example:

class Eggs(GObject.GObject):
    @GObject.Signal
    def spam(self, count:int):
        pass

https://bugzilla.gnome.org/show_bug.cgi?id=434924

1 files changed, 24 insertions, 10 deletions

diff --git a/examples/signal.py b/examples/signal.py
index 9a9d00cc..69c1d624 100644
--- a/examples/signal.py
+++ b/examples/signal.py
@@ -1,28 +1,42 @@
+from __future__ import print_function
+
 from gi.repository import GObject
 
 
 class C(GObject.GObject):
-    __gsignals__ = {
-        'my_signal': (GObject.SIGNAL_RUN_FIRST, GObject.TYPE_NONE,
-                      (GObject.TYPE_INT,))
-    }
+    @GObject.Signal(arg_types=(int,))
+    def my_signal(self, arg):
+        """Decorator style signal which uses the method name as signal name and
+        the method as the closure.
 
-    def do_my_signal(self, arg):
-        print "C: class closure for `my_signal' called with argument", arg
+        Note that with python3 annotations can be used for argument types as follows:
+            @GObject.Signal
+            def my_signal(self, arg:int):
+                pass
+        """
+        print("C: class closure for `my_signal' called with argument", arg)
+
+    @GObject.Signal
+    def noarg_signal(self):
+        """Decoration of a signal using all defaults and no arguments."""
+        print("C: class closure for `noarg_signal' called")
 
 
 class D(C):
     def do_my_signal(self, arg):
-        print "D: class closure for `my_signal' called.  Chaining up to C"
-        C.do_my_signal(self, arg)
+        print("D: class closure for `my_signal' called.  Chaining up to C")
+        C.my_signal(self, arg)
+
 
+def my_signal_handler(obj, arg, *extra):
+    print("handler for `my_signal' called with argument", arg, "and extra args", extra)
 
-def my_signal_handler(object, arg, *extra):
-    print "handler for `my_signal' called with argument", arg, "and extra args", extra
 
 inst = C()
 inst2 = D()
 
 inst.connect("my_signal", my_signal_handler, 1, 2, 3)
+inst.connect("noarg_signal", my_signal_handler, 1, 2, 3)
 inst.emit("my_signal", 42)
+inst.emit("noarg_signal")
 inst2.emit("my_signal", 42)