def load(self, filename, create_if_missing=True):
        filename = Path(filename)
        if not filename.exists() and create_if_missing:
            self.load_pip_requirements()
            with filename.open("w") as f:
                f.write(yaml.dump(self.serialized, default_flow_style=False,
                                  encoding=None))
            self.filename = filename
            return self.save(filename)
        with filename.open() as f:
            for group, requirements in yaml.load(f.read()).items():
                for requirement in requirements:
                    self[group].add(Requirement.coerce(requirement))
        self.filename = filename
def handleevent(self):
        """
        Event-handler for the 'widgets' demo
        """
        while True:
            event = self.dialog.waitForEvent()
            if event.eventType() == yui.YEvent.CancelEvent:
                self.dialog.destroy()
                break
            if event.widget() == self.closebutton:
                info = Info("Quit confirmation", 1, "Are you sure you want to quit?")
                if self.ask_YesOrNo(info):
                    self.dialog.destroy()
                    break
            if event.widget() == self.aboutbutton:
                self.aboutDialog()