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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 url(self):
 """ Returns url for accessing stage instance. """

        return "{server_url}/go/pipelines/{pipeline_name}/{pipeline_counter}/{stage_name}/{stage_counter}".format(
            server_url=self._session.server_url,
            pipeline_name=self.pipeline_name,
            pipeline_counter=self.pipeline_counter,
            stage_name=self.data.name,
            stage_counter=self.data.counter,
        )