'WSGI callable to begin the HTTP response.'

def start_response(self, status, headers, exc_info=None):

    if (self.started_response and (not exc_info)):
        raise AssertionError('WSGI    start_response    called    a    second    time    with    no    exc_info.')
    if self.sent_headers:
        try:
            raise exc_info[0], exc_info[1], exc_info[2]
        finally:
            exc_info = None
    self.started_response = True
    self.status = status
    self.outheaders.extend(headers)
    return self.write
