python -m visdom.server

Then run the code, the result is an error, and the following information appears:

 raise ConnectionError(e, request=request)
requests.exceptions.ConnectionError: 
HTTPConnectionPool(host='localhost', port=8097): 
Max retries exceeded with url: /events (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f6734182d50>: 
Failed to establish a new connection: 
[Errno 111] Connection refused'))

After Baidu, I found the solution:

Finished running the command: python -m visdom.serve, the following sentence will appear:

Setting up a new session...

To keep the terminal on this page, create a new terminal and run the network code in the new terminal.

Then open the link in the browser:

http://localhost:8097/

You can see the curve being drawn.