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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 list(self, service_name, **params):
 """ convinent access method for list. service_name describes the endpoint to call the `list` function on. images.list or apks.list. """

        result = self._invoke_call(service_name, 'list', **params)
        if result is not None:
            return result.get(service_name, list())
        return list()