<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_spec(self) -> dict: """Fetches the OpenAPI spec from the server. If the spec has already been fetched, the cached version is returned instead. ArgS: None Returns: OpenAPI spec data """

        if self.spec:
            return self.spec
        self.spec = requests.get(self.SPEC_URL.format(self.version)).json()
        return self.spec