def get_form_class(self):
        """
        Returns the form class to use in this view.
        """
        if self.form_class is not None:
            return self.form_class

        msg = "'%s' must either define 'form_class' or override 'get_form_class()'"
        raise ImproperlyConfigured(msg % self.__class__.__name__)

        Returns the form class to use in this view.
        
vanilla/views.py