code: def from_stream(credential_filename):
          
          if credential_filename and os.path.isfile(credential_filename):
              try:
                  return _get_application_default_credential_from_file(
                      credential_filename)
              except (ApplicationDefaultCredentialsError, ValueError) as error:
                  extra_help = (' (provided as parameter to the '
                                'from_stream() method)')
                  _raise_exception_for_reading_json(credential_filename,
                                                    extra_help,
                                                    error)
          else:
              raise ApplicationDefaultCredentialsError(
                  'The parameter passed to the from_stream() '
                  'method should point to a file.')
docs: Create a Credentials object by reading information from a file.
  
          It returns an object of type GoogleCredentials.
  
          Args:
              credential_filename: the path to the file from where the
                                   credentials are to be read
  
          Raises:
              ApplicationDefaultCredentialsError: raised when the credentials
                                                  fail to be retrieved.