How to run CGI “hello world” with python http.server

Question

From the http.server docs:

CGIHTTPRequestHandler can be enabled in the command line by passing
the --cgi option:

$ python3 -m http.server --bind localhost --cgi 8000

Put your script into cgi_directories:

This defaults to ['/cgi-bin', '/htbin'] and describes directories to treat as containing CGI scripts.

Open in the browser:

$ python -mwebbrowser http://localhost:8000/cgi-bin/hello.py

where hello.py:

#!/usr/bin/env python3
print("Content-Type: text/html\n")
print("<!doctype html><title>Hello</title><h2>hello world</h2>")

I had to make it executable on POSIX: chmod +x cgi-bin/hello.py.