def update_visible(self):
        """Update and/or sensibly generate a set of visible headers."""
        for header in self._visible.keys():
            if header in self:
                self._visible.replace_header(header, self[header])
            else:
                del self._visible[header]
        for header in ('Date', 'From', 'Reply-To', 'To', 'CC', 'Subject'):
            if header in self and header not in self._visible:
                self._visible[header] = self[header]
dataset/ETHPy150Open babble/babble/include/jython/Lib/mailbox.py/BabylMessage.update_visible/original