code: def headerlist(self):
          
          out = []
          headers = list(self._headers.items())
          if 'Content-Type' not in self._headers:
              headers.append(('Content-Type', [self.default_content_type]))
          if self._status_code in self.bad_headers:
              bad_headers = self.bad_headers[self._status_code]
              headers = [h for h in headers if h[0] not in bad_headers]
          out += [(name, val) for (name, vals) in headers for val in vals]
          if self._cookies:
              for c in self._cookies.values():
                  out.append(('Set-Cookie', _hval(c.OutputString())))
          if py3k:
              out = [(k, v.encode('utf8').decode('latin1')) for (k, v) in out]
          return out
docs: WSGI conform list of (header, value) tuples.