1. Spawn python shell

python3 -c 'import pty; pty.spawn("/bin/bash")'

# if only Python 2:
python -c 'import pty; pty.spawn("/bin/bash")'

python -c 'import subprocess; subprocess.run(["/bin/bash"])'

2. When you background the shell (CTRL+Z) after spawning /bin/bash, use:

stty raw -echo; fg

# if nano or other commands return "Error opening terminal: unknown":
# inside the target shell run this command:

echo $TERM        # probably will return 'dumb'

export TERM=xterm # this should fix it

3. Now your shell is upgraded.

Script (reliable)

script -qc /bin/bash /dev/null