JD Smith <jdtsmith@gmail.com> writes:

>  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.

After typing "1" in 4) and "7" in 6), the buffer looks like: