"can't open file 'extract_scene.py': [Errno 2] No such file or directory" error on a macbook pro

I am working through Brian Howell's very clear tutorial on how to get started. I get stuck at the Step 9 with the command:

> python3 extract_scene.py example_scenes.py SquareToCircle -pl

Which evokes the following response:

>/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.7/Resources/Python.app/Contents/MacOS/Python: can't open file 'extract_scene.py': [Errno 2] No such file or directory

It is clear that it is looking in the wrong place for the file but I have no idea how to tell it where it should be looking.

I am on a mid-2014 MacBook Pro running Catalina 10.15.1.
I am very experienced with R but have not used Python or Terminal.