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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 keyring_auth(username=None, region=None, authenticate=True):
 """ Use the password stored within the keyring to authenticate. If a username is supplied, that name is used; otherwise, the keyring_username value from the config file is used. If there is no username defined, or if the keyring module is not installed, or there is no password set for the given username, the appropriate errors will be raised. If the region is passed, it will authenticate against the proper endpoint for that region, and set the default region for connections. """

    if not keyring:
        # Module not installed
        raise exc.KeyringModuleNotInstalled("The 'keyring' Python module is "
                "not installed on this system.")
    if username is None:
        username = settings.get("keyring_username")
    if not username:
        raise exc.KeyringUsernameMissing("No username specified for keyring "
                "authentication.")
    password = keyring.get_password("pyrax", username)
    if password is None:
        raise exc.KeyringPasswordNotFound("No password was found for the "
                "username '%s'." % username)
    set_credentials(username, password, region=region,
            authenticate=authenticate)