What executes the Python script I see in my browser?

What is playing a Python animation I activate on a remote website? If my browser cannot interpret a local .py file, I would think it also cannot interpret a remote file? Or is it actually the remote website interpreting the script and just sending graphics to me (which would surprise me as there is absolutely no lagging).

The background is this: I visited a website with nice python animations that I could click on and play in my Chrome browser. The site allowed me to to download the scripts as .py files and I would like to edit and play them. However, when I paste the link to such a .py file on my desktop it just opens as a text file. I understand from other posts here that it is because I need to invoke a Python server, which is fair enough. I have searched for python.exe on my own Windows PC, but don't have it. But still I can see python animations on the remote site...