code: def check_credentials(self):
          
          try:
              return bool(self.mturk.get_account_balance())
          except NoCredentialsError:
              raise MTurkServiceException("No AWS credentials set!")
          except ClientError:
              raise MTurkServiceException("Invalid AWS credentials!")
          except Exception as ex:
              raise MTurkServiceException(
                  "Error checking credentials: {}".format(str(ex))
              )
docs: Verifies key/secret/host combination by making a balance inquiry