The environment variables of the shell are in Python via a dictionary available:
>>> import os
>>> print(os.environ.keys())
KeysView(environ({'LANG': 'en_US.UTF-8', 'XDG_GREETER_DATA_DIR': '/var/lib/lightdm-data/bernd', 'LC_PAPER': 'en_US.UTF-8', '_': '/usr/bin/python3', 'SELINUX_INIT': 'YES', ...
>>> print(os.environ['SHELL'])
/bin/bash
They can be changed like regulary dictionary entries:
>>> os.environ['LANG'] = 'en_US.UTF-8'