python-dotenv

python-dotenv package can handle environment variables that you put in a .env file

CONFIG_PATH=${HOME}/.config/foo
DOMAIN=example.org
EMAIL=admin@${DOMAIN}

gitignore this .env

from dotenv import load_dotenv
load_dotenv()

import os
SECRET_KEY = os.getenv("EMAIL")
DATABASE_PASSWORD = os.getenv("DATABASE_PASSWORD")

flask run auto does this