The extension on the file has to be
.sublime-build or Sublime won’t know that it’s supposed to be a build file. It also has to be contained anywhere within a Package, generally your
User package would be where you would put it unless you’re a package author.
To find that location,
Preferences: Browse Packages in the command palette or from the menu; in the window that opens up, the folder named
User is the one you want. Anywhere inside of that folder is fine, should you want to keep things in some structure.
It will appear in the
Tools > Build System menu with the name you gave the file, so if the file is named
MyCoolBuild.sublime-build, it will appear as
MyCoolBuild in the menu.
Should you want to create your own build system for Python it’s thus important to give the file a name like
My Python.sublime-build or
Custom Python.sublime-build or similar because if you just name it
Pythons.sublime-build there will be two entries in the menu, the one that ships with Sublime and yours, and distinguishing them would be problematic.
The location of the install doesn’t really matter for your case here, the only important thing is that Sublime knows where to find it when the time comes (which is where things like the
PATH and so on come into play).
All else being equal, unlike previous versions of Sublime, in Sublime Text 4 so long as you have installed a “normal” version of Python (that is, not Anacona or Miniconda or similar) and you didn’t go out of your way in the Python installer to turn off default options, the
Python.sublime-build that ships with ST
4 will work out of the box for anyone on Windows, Linux or MacOS that wants to execute Python 3 code unless you need very specific command line arguments, options, or other setup.
As such, depending on what you’re trying to do or when the book was written that you’re following, it’s entirely likely that it’s telling you to take a step that you don’t actually need to take and it’s just making things more complicated than it needs to be. A verification of that would be to create a file such as:
Save it on your Desktop as
hello.py, then use
Tools > Build With..., and select the build labeled
Python - Check Syntax) and see if the code executes and prints the version of Python you expect.