code: def _load_version(cls, unpickler, version):
          
          obj = unpickler.load()
          return TransformerChain(obj._state["steps"])
docs: An function to load an object with a specific version of the class.
  
          Parameters
          ----------
          pickler : file
              A GLUnpickler file handle.
  
          version : int
              A version number as maintained by the class writer.