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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 converge(self, playbook=None, **kwargs):
 """ Executes ``ansible-playbook`` against the converge playbook unless specified otherwise and returns a string. :param playbook: An optional string containing an absolute path to a playbook. :param kwargs: An optional keyword arguments. :return: str """

        if playbook is None:
            pb = self._get_ansible_playbook(self.playbooks.converge, **kwargs)
        else:
            pb = self._get_ansible_playbook(playbook, **kwargs)

        return pb.execute()