from http.server import ThreadingHTTPServer, BaseHTTPRequestHandler
import time
class Handler(BaseHTTPRequestHandler):
    def do_GET(self):
        time.sleep(20)
        try:
            self.send_response(200)
            self.end_headers()
            self.wfile.write(b"<title>Slow navigation reproduction</title>Ready")
        except BrokenPipeError:
            pass
ThreadingHTTPServer(("127.0.0.1", 1337), Handler).serve_forever()