Connecting signal with lambda does not work in some cases?

Question

i'm experimenting pygtk programms development, with python 2.7, and i have a little problem when connecting signals using a lambda function :

• let us say that the class which wants to connect a signal is the class A_Class, and the signal is the string "A_Signal"
• we also dispose of a second class B_class defining public function manage_signal
• A_Class dispose of an instance instance_b of B_class

So, here my problem: I don't understand why :

• if i call connect("A_Signal", lambda <signal_parameters> : instance_b.manage_signal) from a method of A_Class instance => we can't even enter in function manage_signal of instance_b (for example : connect("activate", lambda menu_item : instance_b.manage_signal)
• if i define in A_Class a method manage_signal, which in turn call instance_b.manage_signal and call connect("A_Signal", lambda <signal_parameters> : self.manage_signal) => this time it works ?

Here some code to be more explicit

   class A_Class(gtk.Window):

       def __init__(self):
           super(gtk.Window, self).__init__()
           self.__instance_b = B_Class()
           # this does not work and i don't understand why
           self.connect("delete-event", lambda the_widget,the_event: self.__instance_b.manage_event)
           # this works
           self.connect("delete-event", self.__manage_event)

       def __manage_event(self):
           self.__instance_b.manage_event

   class B_Class(object):

        def manage_event(self):
            # do some stuffs ...

Regards

Answer 1

Your lambda expression should call the handler function instead of returning it:

self.connect("delete-event", lambda the_widget, the_event: \
    self.__instance_b.manage_event(the_widget, the_event))

Of course, as you said, this is unneeded because it's equivalent to:

self.connect("delete-event", self.__instance_b.manage_event)

The lambda would only end up relaying the signal arguments to manage_event(), something that connect() can perfectly do by itself.