bug#49073: 28.0.50; python-send-to-repl functions misbehave

[dalanicolai]

This is a combined bug report for two unrelated but still somewhat
related bugs.

- The first bug is that when using `python-send-to-repl` functions, the
  input does not get printed in the REPL buffer.
- The second bug is that for various setups, even the output does not
  get printed properly.

The reason for this bug report, which might arguably have the best
description, is
the Spacemacs issue at
https://github.com/syl20bnr/spacemacs/issues/14845.

Start emacs with -Q flag. Open a python buffer/.py file.
Call `M-x run-python`
type e.g. 2+2
now send to REPL with `M-x python-shell-send-buffer/statement`

The input does not get printed in the REPL (as I would expect from
sending to REPL).  This could be intentionally, but I would say that at
least `python-shell-send-statement` should print also the input.

Then secondly, often, even the output does not get printed (when
not sending an explicit print statement).
This seems to occur when sending more then two lines (e.g. when using
`python-shell-send-buffer` in a buffer that
starts with an empty line and has 2+2 on the second line). So then the
'interactivity` of using the repl got totally lost.This is a combined
bug report for two unrelated but still somewhat related bugs.

- The first bug is that when using `python-send-to-repl` functions, the
input
  does not get printed in the REPL buffer. - The second bug is that for
various
  setups, even the output does not get printed properly.

The reason for this bug report is the Spacemacs issue at
https://github.com/syl20bnr/spacemacs/issues/14845.

To reproduce:

- Start emacs with -Q flag.
- Open a python buffer/.py file.
- Call `M-x run-python`
- type e.g. 2+2 and send to REPL with `M-x python-shell-send-
buffer/statement`

The INPUT does not get printed in the REPL (as I would expect from
sending to
REPL). This could be intentionally, but I would say that at least
`python-shell-send-statement` should print also the input.

Then secondly, often, even the output does not get printed (when
not sending an explicit print statement).
This seems to occur when sending more then two lines (e.g. when using
`python-shell-send-buffer` in a buffer that
starts with an empty line and has 2+2 on the second line). So then the
'interactivity` of using the REPL got totally lost.


In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
3.24.25, cairo version 1.16.0)
 of 2021-02-18 built on daniel-fedora
Repository revision: 185121da6978553d538d37d6d0e67dc52e13311f
Repository branch: feature/native-comp
Windowing system distributor 'The X.Org Foundation', version
11.0.12011000
System Description: Fedora 34 (Workstation Edition)

Configured using:
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