code: def get_backend_symbol(self, backend):
          
          out = SymbolHandle()
          check_call(_LIB.MXGenBackendSubgraph(self.handle, c_str(backend), ctypes.byref(out)))
          return Symbol(out)
docs: Return symbol for target backend.
  
          Parameters
          ----------
          backend : str
              The backend names.
  
          Returns
          -------
          out : Symbol
              The created Symbol for target backend.