eventlet.wsgi 中的 start_response定义

        def start_response(status, response_headers, exc_info=None):
            status_code[0] = status.split()[0]
            if exc_info:
                try:
                    if headers_sent:
                        # Re-raise original exception if headers sent
                        raise exc_info[0], exc_info[1], exc_info[2]
                finally:
                    # Avoid dangling circular ref
                    exc_info = None

            capitalized_headers = [('-'.join([x.capitalize()
                                              for x in key.split('-')]), value)
                                   for key, value in response_headers]

            headers_set[:] = [status, capitalized_headers]
            return write

如果调用eventlet.wsgi来开启服务，那么最上层的start_response函数就是这个，值得注意的就是

capitalized_headers，
换言之，在整个应用的header都会被格式化成Content-Type这种首字母大写的格式。