def backtrack(self, source):
        """Given a unique key in the store, recreate original source"""
        key = self.get_tok(source)
        s = self[key]()
        meta = s.metadata['original_source']
        cls = meta['cls']
        args = meta['args']
        kwargs = meta['kwargs']
        cls = import_name(cls)
        sout = cls(*args, **kwargs)
        sout.metadata = s.metadata['original_metadata']
        sout.name = s.metadata['original_name']
        return sout
Given a unique key in the store, recreate original source