def remove(self, elem):
        """Remove a requirement.

        :param elem: a string or :class:`Requirement` instance.
        """
        if isinstance(elem, text_type):
            for requirement in self:
                if requirement.package == elem:
                    return super(Requirements, self).remove(requirement)
        return super(Requirements, self).remove(elem)
def _get_selected_path(self):
        """
        Helper function to get the selected path

        @return Gtk.TreePath : returns exactly one path for the selected object
                               or None
        """
        selection = self.get_selection()
        if selection:
            model, selected_paths = self.get_selection().get_selected_rows()
            if selected_paths:
                return selected_paths[0]
        return None