Simplifying PyGTK signals in Python

This is a followup to my previous post.

A fairly common pattern in GTK code seems to be updating a widget whenever a value changes in your controller. That is, something like this:

class Counter(gobject.Gobject):
__gsignals__ = {
    'counter-changed': (gobject.SIGNAL_RUN_FIRST,
                        gobject.TYPE_NONE, (int,)),
}

def __init__(self):
    self.counter = 0

def inc(self):
self.counter += 1
    self.emit('counter-changed', self.counter)

def dec(self):
self.counter -= 1
    self.emit('counter-changed', self.counter)

Needless to say, this can get a bit tedious. With a bit of stack frame hackery we can reduce that boilerplate to the following:

class Counter(gobject.GObject):
counter = SignalProperty('counter-changed', 0)

def inc(self):
self.counter += 1

def dec(self):
self.counter -= 1

Here's the code:

class SignalProperty(object):
def __init__(self, name, default=None):
    self.name = name
    self.default = default
    frame = sys._getframe(1)
    locals_ = frame.f_locals
    signals = locals_.setdefault('__gsignals__', {})
    signals[name] = (gobject.SIGNAL_RUN_FIRST,
               gobject.TYPE_NONE, (object,))

def __get__(self, instance, owner):
    if instance is None:
      return self
    return getattr(instance, '_signal_' + self.name, self.default)

def __set__(self, instance, value):
    setattr(instance, '_signal_' + self.name, value)
    instance.emit(self.name, value)

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