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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 human_id(self):
 """Subclasses may override this to provide a pretty ID which can be used for bash completion. """

        if self.NAME_ATTR in self.__dict__ and self.HUMAN_ID:
            return utils.to_slug(getattr(self, self.NAME_ATTR))
        return None