Hi!

- I'm pretty sure I'm on the master branch. I don't clone from git, but I
compared my version of python.el with this
https://github.com/emacs-mirror/emacs/commit/6cfc312d7196d7c7c70e7030b344891ecea8c4f1#diff-f808b0589744f83f41d9f581e8b07001145598d2a2aa07fd40c1d20ee35df762
and it looks up to date.

- Regarding the recursive calls, I tried to look into it, and what I found was very confusing.
  - The tests I sent on number of characters, I believe establish that the issue only arises when the string is long enough for python-shell-send-string to save to a file and call python-shell-send file.
  - The backtrace - I sent to you. I suppose it's hard to decipher.
  - I then tried setting a breakpoint in 'python-shell-send-string. If I step through commands there, I see myself looping through this function again and again (creating more and more files, which is eventually what leads to the error). Buf *if* I step into 'python-shell-send-file when going through the difference expressions of 'python-shell-send-string, I get into the function (which indeed calls 'comint-send-string, not 'python-shell-send-string... and at this point, instead of returning to the *beginning* of python-shell-send string, I end up exiting python-shell-send-string and everything works.
      - In other words, the problem does not arise in edebug mode *if* I step into python-shell-send-file when python-shell-send-string calls it.

This is very weird, sounds like perhaps some async issue... Very odd.