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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_sub_package_provider_session(self, sub_package, session_name, proxy=None):
 """Gets the session from a sub-package"""

        agent_key = self._get_agent_key()
        if session_name in self._provider_sessions[agent_key]:
            return self._provider_sessions[agent_key][session_name]
        else:
            manager = self._get_sub_package_provider_manager(sub_package)
            session = self._instantiate_session('get_' + session_name + '_for_bank',
                                                proxy=self._proxy,
                                                manager=manager)
            self._set_bank_view(session)
            self._set_object_view(session)
            self._set_operable_view(session)
            self._set_containable_view(session)
            if self._session_management != DISABLED:
                self._provider_sessions[agent_key][session_name] = session
            return session