def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def add_backend(self, backend):
        """
        Adds a new backend to the list

        @param backend_id: the id of the backend to add
        """
        if backend:
            backend_iter = self.liststore.append([
                backend.get_id(),
                self.dialog.get_pixbuf_from_icon_name(backend.get_icon(),
                                                      16),
                backend.get_human_name(),
                self._get_markup_for_tags(backend.get_attached_tags()),
            ])
            self.backendid_to_iter[backend.get_id()] = backend_iter