How to block and prohibit web crawlers in Nginx server

location / {
  if ($http_user_agent ~* "python|curl|java|wget|httpclient|okhttp") {
    return 503;
  }
  # Other normal configuration...
}

server { 
    listen 80; 
    server_name www.xxx.com; 
    #charset koi8-r; 
    #access_log logs/host.access.log main; 
    #location / { 
    #root html; 
    # index index.html index.htm; 
    #} 
  if ($http_user_agent ~* "qihoobot|Baiduspider|Googlebot|Googlebot-Mobile|Googlebot-Image|Mediapartners-Google|Adsbot-Google|Feedfetcher-Google|Yahoo! Slurp|Yahoo! Slurp China|YoudaoBot|Sosospider|Sogou spider|Sogou web spider|MSNBot|ia_archiver|Tomato Bot") { 
        return 403; 
    } 
  location ~ ^/(.*)$ { 
        proxy_pass http://localhost:8080; 
    proxy_redirect off; 
    proxy_set_header Host $host; 
    proxy_set_header X-Real-IP $remote_addr; 
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; 
    client_max_body_size 10m; 
    client_body_buffer_size 128k; 
    proxy_connect_timeout 90; 
    proxy_send_timeout 90; 
    proxy_read_timeout 90; 
    proxy_buffer_size 4k; 
    proxy_buffers 4 32k; 
    proxy_busy_buffers_size 64k; 
    proxy_temp_file_write_size 64k; 
  } 
    #error_page 404 /404.html; 
    # redirect server error pages to the static page /50x.html 
    # 
    error_page 500 502 503 504 /50x.html; 
    location = /50x.html { 
      root html; 
    } 
    # proxy the PHP scripts to Apache listening on 127.0.0.1:80 
    # 
    #location ~ \.php$ { 
    # proxy_pass http://127.0.0.1; 
    #} 
    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000 
    # 
    #location ~ \.php$ { 
    #root html; 
    # fastcgi_pass 127.0.0.1:9000; 
    # fastcgi_index index.php; 
    # fastcgi_param SCRIPT_FILENAME /scripts$fastcgi_script_name; 
    #include fastcgi_params; 
    #} 
    # deny access to .htaccess files, if Apache's document root 
    # concurs with nginx's one 
    # 
    #location ~ /\.ht { 
    # deny all; 
    #} 
  }

curl -I -A "qihoobot" www.xxx.com