code: def load_host_keys(self, filename):
          
          self._host_keys_filename = filename
          self._host_keys.load(filename)
docs: Load host keys from a local host-key file.  Host keys read with this
          method will be checked after keys loaded via `load_system_host_keys`,
          but will be saved back by `save_host_keys` (so they can be modified).
          The missing host key policy `.AutoAddPolicy` adds keys to this set and
          saves them, when connecting to a previously-unknown server.
  
          This method can be called multiple times.  Each new set of host keys
          will be merged with the existing set (new replacing old if there are
          conflicts).  When automatically saving, the last hostname is used.
  
          :param str filename: the filename to read
  
          :raises: ``IOError`` -- if the filename could not be read