On Apr 13, 2021, at 4:05 AM, Lars Ingebrigtsen <larsi@gnus.org> wrote:

JD Smith <jdtsmith@gmail.com> writes:

Do you have a step-by-step recipe, starting from "emacs -Q", to
reproduce this problem?

1 emacs -Q
2 M-x run-python
3 C-x 5 b “ *Python-font-lock*”
4 In inferior python shell: type any line.
5 C-c SPC (`comint-accumulate’) to continue.
6 Type another line. Notice the first line is repeated.
7 Repeat steps 5 & 6 several times.

You didn't say what Emacs version you're using -- I tested this in Emacs
28, and was unable to reproduce this. The " *Python-font-lock*" buffer
never contains more than a single non-blank line using this recipe.
(The "any line" I used to test was "5”.)

Mac port, v27.2, python-mode v0.26.1. I have a hard time understanding how this would not reproduce, as (buffer-substring-no-properties prompt-end (point-max)) clearly takes all of the text (multi-lines included) from the prompt onward. I took a look here (python-mode v0.27.1) and the input is gathered in the same manner in the post-command-hook. The “repeated” lines in #6 are in the *Python-font-lock* buffer, btw.