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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ensure_signed_credentials(credentials):
 """Raise AttributeError if the credentials are unsigned. :type credentials: :class:`google.auth.credentials.Signing` :param credentials: The credentials used to create a private key for signing text. :raises: :exc:`AttributeError` if credentials is not an instance of :class:`google.auth.credentials.Signing`. """

    if not isinstance(credentials, google.auth.credentials.Signing):
        auth_uri = (
            "https://google-cloud-python.readthedocs.io/en/latest/"
            "core/auth.html?highlight=authentication#setting-up-"
            "a-service-account"
        )
        raise AttributeError(
            "you need a private key to sign credentials."
            "the credentials you are currently using %s "
            "just contains a token. see %s for more "
            "details." % (type(credentials), auth_uri)
        )