Where do I set my environment variables using python?

I recently created a flask app and uploaded it successfully to a webapp directory created on Webfaction. I stored credentials into environment variables in my apache's bin/start script. After inserting configuration code (down below) into my former basic flask app, which contained nothing more than a route to '/' and a message that said "Hello world", I immediately got a 500 internal server error. What am I doing wrong here? And how do I fix this?

init.py

 app.config.update(dict(
        DEBUG = True,
        MAIL_SERVER = 'SERVER_GOES_HERE'',
        MAIL_PORT = PORT_GOES_HERE,
        MAIL_USE_TLS = BOOL_GOES_HERE,
        MAIL_USE_SSL = BOOL_GOES_HERE,
        MAIL_USERNAME = os.environ['USER'],
        MAIL_PASSWORD = os.environ['PASS'],
    ))

start

#!/bin/bash

export USER=USERNAMEGOESHERE
export PASS=PASSGOESHERE

LD_LIBRARY_PATH= DEFAULT_CONTENT_GOES_HERE

error logs (simplified to show details)

File "/home/username/webapps/myapp/wsgi.py", line 3, in <module>
   from myapp import app as application

   File "/home/username/webapps/myapp/myapp/__init__.py", line 32, in <module>
   MAIL_USERNAME = os.environ['USER'],

   File "/usr/lib64/python2.7/UserDict.py", line 23, in __getitem__
    raise KeyError(key)
    KeyError: 'USER'