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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 validate(self):
 """ Check the value of the config attributes. """

        for client in self.clients:
            for key in REQUIRED_KEYS:
                if key not in client:
                    raise MissingConfigValue(key)

            if 'revision_file' not in client:
                client.revision_file = DEFAULT_REVISION_FILEPATH.format(
                    client.key
                )