This chunk of docs has bad info in both Python2 and Python3 docs:

4.1.3. Configuration

Python on OS X honors all standard Unix environment variables such as PYTHONPATH, but setting these variables for programs started from the Finder is non-standard as the Finder does not read your .profile or .cshrc at startup. You need to create a file ~/.MacOSX/environment.plist. See Apple’s Technical Document QA1067 for details.

If you search for QA1067, you are informed that the document is legacy and unsupported, with a suggestion for where to look now. That suggested link leads to a 404.

Searching the apple site, I find that at least some thoughtful developers think that configuring the environment isn't even possible, generally; and isn't considered good form even if so. Here:
https://forums.developer.apple.com/message/217422

I have no problem setting things for my terminal, as a longtime (unix) user, but for others, this section probably needs a complete examination with an eye toward making it current. quite possibly by reorganizing it.

Thanks for the reminder.  Yes, the whole "Using Python on a Macintosh" section is very much out-of-date and needs a complete rewrite.  It has been on my To Do list for a long time; I'll see what I can do to expedite it.