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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 get_request_token(self):
 """ Return the request token for this API. If we've not fetched it yet, go out, request and memoize it. """

        
        if self._request_token is None:
            self._request_token = self._get_request_token()
        return self._request_token