langchain/vectorstores/faiss.py/FAISS/similarity_search_with_score_by_vector
class FAISS:    def similarity_search_with_score_by_vector(
        self, embedding: List[float], k: int = 4
    ) -> List[Tuple[Document, float]]:
        """Return docs most similar to query.

        Args:
            embedding: Embedding vector to look up documents similar to.
            k: Number of Documents to return. Defaults to 4.

        Returns:
            List of Documents most similar to the query and score for each
        """
        faiss = dependable_faiss_import()
        vector = np.array([embedding], dtype=np.float32)
        if self._normalize_L2:
            faiss.normalize_L2(vector)
        scores, indices = self.index.search(vector, k)
        docs = []
        for j, i in enumerate(indices[0]):
            if i == -1:
                # This happens when not enough docs are returned.
                continue
            _id = self.index_to_docstore_id[i]
            doc = self.docstore.search(_id)
            if not isinstance(doc, Document):
                raise ValueError(f"Could not find document for id {_id}, got {doc}")
            docs.append((doc, scores[0][j]))
        return docs