Hi!

I believe this commit:

2021-09-21 "Make syntax-ppss more accurate for Python triple quotes
(bug#49518)" (0646c68171)

… introduced a regression for users who set python-forward-sexp-function
to nil (or users who set forward-sexp-function buffer-locally, as was
suggested by python.el's commentary before Emacs 28.1).

To reproduce:

$ echo '"""Quotes for days"""' > repro.py
$ emacs -Q -eval '(setq python-forward-sexp-function nil)' repro.py
; C-M-f

- Point should move to position 22,
- As of the above commit, it lies at position 3.

(Note: if one visits the file before setting the user option, the
setting will not be taken into account; to reproduce, one should then
either set forward-sexp-function directly, or revert the buffer)

I've attached an ert test for this recipe; it passes when run against
0646c68171^ (i.e. the parent commit) and fails as of 0646c68171.

I haven't started to dig into what the change meant to fix, so I cannot
say whether TRT would be to keep the change and improve on it or revert
the change and fix the original problem some other way.

Let me know if I can assist further; thanks for your time.