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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 flex_api(self):
 """ Access the FlexApi Twilio Domain :returns: FlexApi Twilio Domain :rtype: twilio.rest.flex_api.FlexApi """

        if self._flex_api is None:
            from twilio.rest.flex_api import FlexApi
            self._flex_api = FlexApi(self)
        return self._flex_api