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

        if self._execution_context is None:
            self._execution_context = ExecutionContextList(
                self._version,
                flow_sid=self._solution['flow_sid'],
                execution_sid=self._solution['sid'],
            )
        return self._execution_context