def to_unicode_dict(self):
        """ Return headers as a CaselessDict with unicode keys
        and unicode values. Multiple values are joined with ','.
        """
        return CaselessDict(
            (to_unicode(key, encoding=self.encoding),
             to_unicode(b','.join(value), encoding=self.encoding))
            for key, value in self.items())
 Return headers as a CaselessDict with unicode keys
        and unicode values. Multiple values are joined with ','.
        
stackoverflow/venv/lib/python3.6/site-packages/scrapy/http/headers.py