code: def cd(self, path=None):
          
          if path is None:
              return lock_and_call(
                  lambda: self._impl.cd(),
                  self._lock
              )
          else:
              return lock_and_call(
                  lambda: self._impl.cd(path),
                  self._lock
              )
docs: Get or set the current working directory from the underlying
          interpreter (see https://en.wikipedia.org/wiki/Working_directory).
  
          Args:
              path: New working directory or None (to display the working
              directory).
  
          Returns:
              Current working directory.