google.auth.credentials.Credentials: Credentials to use for queries
        performed through IPython magics

        Note:
            These credentials do not need to be explicitly defined if you are
            using Application Default Credentials. If you are not using
            Application Default Credentials, manually construct a
            :class:`google.auth.credentials.Credentials` object and set it as
            the context credentials as demonstrated in the example below. See
            `auth docs`_ for more information on obtaining credentials.

        Example:
            Manually setting the context credentials:

            >>> from google.cloud.bigquery import magics
            >>> from google.oauth2 import service_account
            >>> credentials = (service_account
            ...     .Credentials.from_service_account_file(
            ...         '/path/to/key.json'))
            >>> magics.context.credentials = credentials


        .. _auth docs: http://google-auth.readthedocs.io
            /en/latest/user-guide.html#obtaining-credentials

def credentials(self):
        """google.auth.credentials.Credentials: Credentials to use for queries
        performed through IPython magics

        Note:
            These credentials do not need to be explicitly defined if you are
            using Application Default Credentials. If you are not using
            Application Default Credentials, manually construct a
            :class:`google.auth.credentials.Credentials` object and set it as
            the context credentials as demonstrated in the example below. See
            `auth docs`_ for more information on obtaining credentials.

        Example:
            Manually setting the context credentials:

            >>> from google.cloud.bigquery import magics
            >>> from google.oauth2 import service_account
            >>> credentials = (service_account
            ...     .Credentials.from_service_account_file(
            ...         '/path/to/key.json'))
            >>> magics.context.credentials = credentials


        .. _auth docs: http://google-auth.readthedocs.io
            /en/latest/user-guide.html#obtaining-credentials
        """
        if self._credentials is None:
            self._credentials, _ = google.auth.default()
        return self._credentials