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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def batch_get_documents( self, database, documents, mask=None, transaction=None, new_transaction=None, read_time=None, retry=google.api_core.gapic_v1.method.DEFAULT, timeout=google.api_core.gapic_v1.method.DEFAULT, metadata=None, ):
 """ Gets multiple documents. Documents returned by this method are not guaranteed to be returned in the same order that they were requested. Example: Args: database (str):
 The database name. In the format: ``projects/{project_id}/databases/{database_id}``. documents (list[str]):
 The names of the documents to retrieve. In the format: ``projects/{project_id}/databases/{database_id}/documents/{document_path}``. The request will fail if any of the document is not a child resource of the given ``database``. Duplicate names will be elided. mask (Union[dict, ~google.cloud.firestore_v1beta1.types.DocumentMask]):
 The fields to return. If not set, returns all fields. If a document has a field that is not present in this mask, that field will not be returned in the response. If a dict is provided, it must be of the same form as the protobuf message :class:`~google.cloud.firestore_v1beta1.types.DocumentMask` transaction (bytes):
 Reads documents in a transaction. new_transaction (Union[dict, ~google.cloud.firestore_v1beta1.types.TransactionOptions]):
 Starts a new transaction and reads the documents. Defaults to a read-only transaction. The new transaction ID will be returned as the first response in the stream. If a dict is provided, it must be of the same form as the protobuf message :class:`~google.cloud.firestore_v1beta1.types.TransactionOptions` read_time (Union[dict, ~google.cloud.firestore_v1beta1.types.Timestamp]):
 Reads documents as they were at the given time. This may not be older than 60 seconds. If a dict is provided, it must be of the same form as the protobuf message :class:`~google.cloud.firestore_v1beta1.types.Timestamp` retry (Optional[google.api_core.retry.Retry]):
 A retry object used to retry requests. If ``None`` is specified, requests will not be retried. timeout (Optional[float]):
 The amount of time, in seconds, to wait for the request to complete. Note that if ``retry`` is specified, the timeout applies to each individual attempt. metadata (Optional[Sequence[Tuple[str, str]]]):
 Additional metadata that is provided to the method. Returns: Iterable[~google.cloud.firestore_v1beta1.types.BatchGetDocumentsResponse]. Raises: google.api_core.exceptions.GoogleAPICallError: If the request failed for any reason. google.api_core.exceptions.RetryError: If the request failed due to a retryable error and retry attempts failed. ValueError: If the parameters are invalid. """

        # Wrap the transport method to add retry and timeout logic.
        if "batch_get_documents" not in self._inner_api_calls:
            self._inner_api_calls[
                "batch_get_documents"
            ] = google.api_core.gapic_v1.method.wrap_method(
                self.transport.batch_get_documents,
                default_retry=self._method_configs["BatchGetDocuments"].retry,
                default_timeout=self._method_configs["BatchGetDocuments"].timeout,
                client_info=self._client_info,
            )

        # Sanity check: We have some fields which are mutually exclusive;
        # raise ValueError if more than one is sent.
        google.api_core.protobuf_helpers.check_oneof(
            transaction=transaction,
            new_transaction=new_transaction,
            read_time=read_time,
        )

        request = firestore_pb2.BatchGetDocumentsRequest(
            database=database,
            documents=documents,
            mask=mask,
            transaction=transaction,
            new_transaction=new_transaction,
            read_time=read_time,
        )
        if metadata is None:
            metadata = []
        metadata = list(metadata)
        try:
            routing_header = [("database", database)]
        except AttributeError:
            pass
        else:
            routing_metadata = google.api_core.gapic_v1.routing_header.to_grpc_metadata(
                routing_header
            )
            metadata.append(routing_metadata)

        return self._inner_api_calls["batch_get_documents"](
            request, retry=retry, timeout=timeout, metadata=metadata
        )