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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 cleanup(self, keep=5):
 """Remove all but the ``keep`` most recent releases. If any of the candidates for deletion are pointed to by the 'current' symlink, they will not be deleted. This method performs N + 2 network operations where N is the number of old releases that are cleaned up. :param int keep: Number of old releases to keep around """

        releases = self.get_releases()
        current_version = self.get_current_release()
        to_delete = [version for version in releases[keep:] if version != current_version]

        for release in to_delete:
            self._runner.run("rm -rf '{0}'".format(os.path.join(self._releases, release)))