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 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