code: def _get_implicit_credentials(cls):
          
          # Environ checks (in order).
          environ_checkers = [
              cls._implicit_credentials_from_files,
              cls._implicit_credentials_from_gae,
              cls._implicit_credentials_from_gce,
          ]
  
          for checker in environ_checkers:
              credentials = checker()
              if credentials is not None:
                  return credentials
  
          # If no credentials, fail.
          raise ApplicationDefaultCredentialsError(ADC_HELP_MSG)
docs: Gets credentials implicitly from the environment.
  
          Checks environment in order of precedence:
          - Environment variable GOOGLE_APPLICATION_CREDENTIALS pointing to
            a file with stored credentials information.
          - Stored "well known" file associated with `gcloud` command line tool.
          - Google App Engine (production and testing)
          - Google Compute Engine production environment.
  
          Raises:
              ApplicationDefaultCredentialsError: raised when the credentials
                                                  fail to be retrieved.