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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 server_version(self):
 """ Special method for getting server version. Because of different behaviour on different versions of server, we have to pass different headers to the endpoints. This method requests the version from server and caches it in internal variable, so other resources could use it. :return: server version parsed from `about` page. """

        if self.__server_version is None:
            from yagocd.resources.info import InfoManager
            self.__server_version = InfoManager(self).version

        return self.__server_version