code: def get_project_endpoint_from_env(project_id=None, host=None):
    
    project_id = project_id or os.getenv(_DATASTORE_PROJECT_ID_ENV)
    if not project_id:
      raise ValueError('project_id was not provided. Either pass it in '
                       'directly or set DATASTORE_PROJECT_ID.')
    # DATASTORE_HOST is deprecated.
    if os.getenv(_DATASTORE_HOST_ENV):
      logging.warning('Ignoring value of environment variable DATASTORE_HOST. '
                      'To point datastore to a host running locally, use the '
                      'environment variable DATASTORE_EMULATOR_HOST')
  
    url_override = os.getenv(_DATASTORE_URL_OVERRIDE_ENV)
    if url_override:
      return '%s/projects/%s' % (url_override, project_id)
  
    localhost = os.getenv(_DATASTORE_EMULATOR_HOST_ENV)
    if localhost:
      return ('http://%s/%s/projects/%s'
              % (localhost, API_VERSION, project_id))
  
    host = host or GOOGLEAPIS_HOST
    return 'https://%s/%s/projects/%s' % (host, API_VERSION, project_id)
docs: Get Datastore project endpoint from environment variables.
  
    Args:
      project_id: The Cloud project, defaults to the environment
          variable DATASTORE_PROJECT_ID.
      host: The Cloud Datastore API host to use.
  
    Returns:
      the endpoint to use, for example
      https://datastore.googleapis.com/v1/projects/my-project
  
    Raises:
      ValueError: if the wrong environment variable was set or a project_id was
          not provided.