How can I replace bash with Python?

That thread and its accepted answer in particular are about using Python for shell scripting, not as an interactive shell.

To write scripts in a different language, put e.g. #!/usr/bin/env python instead of #!/bin/bash at the top of your script.

If you want to try out a different interactive shell, just run it, e.g. type ipython at your existing shell prompt. If you've decided to adopt that shell, set the SHELL environment variable at the start of your session (in ~/.profile in most environments, or in ~/.pam_environment), e.g. export SHELL=/usr/bin/ipython (.profile syntax) or SHELL="/usr/bin/ipython" (.pam_environment syntax).

None of the shells that I've seen based on advanced languages such as Perl or Python are good enough for interactive use in my opinion. They're too verbose for common tasks, especially the common job of a shell which is to launch an application. I wrote about a similar topic 4 years ago; I don't think the situation has fundamentally improved since then.

I know this question is quite old now, but there is a new shell based on a superset of Python 3 called xonsh which might be what you are looking for.

from the website:

Xonsh is a Python-ish, BASHwards-looking shell language and command prompt. The language is a superset of Python 3.4+ with additional shell primitives that you are used to from Bash and IPython. It works on all major systems including Linux, Mac OSX, and Windows. Xonsh is meant for the daily use of experts and novices alike.

See it at xon.sh

Rather not

The reason is that Python has no support for dealing with elevated privileges. The worst case is with editing system files.

Compare

sudo sed -i -e "/\#LXC_DOMAIN/ s/\#//" /etc/default/lxc-net

with:

out = subprocess.run('''sudo sed -i -e "/\#LXC_DOMAIN/ s/\#//" /etc/default/lxc-net''', shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT,env={"PATH": "/usr/bin"})

You can't use Python's native file handling for system files, because Python is inherently unable to execute subcommands with elevated privileges.