def _get_client(self, project_id):
if not self._client:<EOL><INDENT>self._client = Client(project=project_id, credentials=self._get_credentials())<EOL><DEDENT>return self._client<EOL>
Provides a client for interacting with the Cloud Spanner API.

:param project_id: The ID of the  GCP project.
:type project_id: str
:return: google.cloud.spanner_v1.client.Client
:rtype: object