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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 executions(self):
 """ Access the executions :returns: twilio.rest.studio.v1.flow.execution.ExecutionList :rtype: twilio.rest.studio.v1.flow.execution.ExecutionList """

        if self._executions is None:
            self._executions = ExecutionList(self._version, flow_sid=self._solution['sid'], )
        return self._executions