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 flush_to_index(self) -> None:
        """Flush changes in our configuration file to the index"""
        assert self._smref is not None
        # should always have a file here
        assert not isinstance(self._file_or_files, BytesIO)

        sm = self._smref()
        if sm is not None:
            index = self._index
            if index is None:
                index = sm.repo.index
            # END handle index
            index.add([sm.k_modules_file], write=self._auto_write)
            sm._clear_cache()
        # END handle weakref