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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_api_url(self, lambda_name, stage_name):
 """ Given a lambda_name and stage_name, return a valid API URL. """

        api_id = self.get_api_id(lambda_name)
        if api_id:
            return "https://{}.execute-api.{}.amazonaws.com/{}".format(api_id, self.boto_session.region_name, stage_name)
        else:
            return None