$ python -m http.server
Serving HTTP on 0.0.0.0 port 8000 ...
Or, for Python2:
$ python -m SimpleHTTPServer
Serving HTTP on 0.0.0.0 port 8000 ...
In this message, Python tells you the IP address (0.0.0.0) and the port number (8000).
So, if the file is named d3_template.html, you can get to this page via http://0.0.0.0:8000/d3_template.html
On most machines you should also be able to use
http://localhost:8000/d3_template.html