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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(self, username=None):
 """ Uses the keyring module to retrieve the user's password or api_key. """

        if not keyring:
            # Module not installed
            raise exc.KeyringModuleNotInstalled("The 'keyring' Python module "
                    "is not installed on this system.")
        if username is None:
            username = pyrax.get_setting("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)
        style = self._creds_style or self._default_creds_style
        # Keyring username may be different than the credentials. Use the
        # existing username, if present; otherwise, use the supplied username.
        username = self.username or username
        if style == "apikey":
            return self.authenticate(username=username, api_key=password)
        else:
            return self.authenticate(username=username, password=password)