code: def raise_io_error(self, errno, filename=None):
          
          raise IOError(errno, self._error_message(errno), filename)
docs: Raises IOError.
          The error message is constructed from the given error code and shall
          start with the error in the real system.
  
          Args:
              errno: A numeric error code from the C variable errno.
              filename: The name of the affected file, if any.