bug#25753: 25.2; Python mode shell interaction not working 100%

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charles@aurox.ch (Charles A. Roelli) writes:
>
> Tested, and it has the same problem.  Here is what *Python* normally
> looks like at the start, run from M-x run-python in emacs -Q:
>
> Python 2.7.12 (v2.7.12:d33e0cf91556, Jun 26 2016, 12:10:39) 
> [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
> Type "help", "copyright", "credits" or "license" for more information.
>>>> import codecs, os;__pyfile =
>>>> codecs.open('''/var/folders/WP/WPe0Q1iAGc0J7iI6J50jcU+++TI/-Tmp-/py16611qgD''',
>>>> encoding='''utf-8''');__code =
>>>> __pyfile.read().encode('''utf-8''');__pyfile.close();os.remove('''/var/folders/WP/WPe0Q1iAGc0J7iI6J50jcU+++TI/-Tmp-/py16611qgD''');exec(compile(__code,
>>>> '''/var/folders/WP/WPe0Q1iAGc0J7iI6J50jcU+++TI/-Tmp-/py16611qgD''',
>>>> 'exec'));
> python.el: native completion setup loaded
>
> It seems like the line starting with ">>> " should not be printed, if
> <nyc4bos@aol.com>'s test output is deemed to be running more or less
> correctly.  Maybe that can point us in the right direction?

Hmm, it's odd, though since you're still getting the "setup loaded"
message, the code *is* getting evaluated anyway, so it's likely that
this problem is not directly related.  Let's see if we can track it down
anyway, try the loading the attached as

    emacs -Q -l py-trace-bad-output.el

and see if anything shows up in *Messages*.

py-trace-bad-output.el
Description: tracing code

>> Can you test the python code from python-shell-completion-native-setup
>> outside of Emacs, e.g., save it to a file called 'native-completion.py'
>> and then run 'python -i native-completion.py' and then type an
>> underscore and hit <tab>.
>
> I get the following:
>
>>>> ___package__
> __PYTHON_EL_native_completion_setup
> __name__
> __doc__
> __import__
> __debug__
>
> Interestingly, none of the dummy completions pop up.

This seems to be the core of the problem.  I gather that macOS uses
libedit instead of readline by default, perhaps that is the source of
incompatibility.  Can you figure out how to change the python code so
that the dummy completions do show up?