title: where Environment variables for python are saved
body: <p>I know to set an environment variable in python is to use os.environ['API_USER'] but where this variable is saved, I supposed this environment variable is saved in .env file but it wasn't.</p>
  
  <p>on the console to retrieve all the environment variables use command: os.environ
  but don't know where are saved. 
  need your help, Thanks!</p>