Poor man's Dependency Injection

di.py

user = None

library.py

import di

def now():
  if not di.user:
    print "Unauthenticated user"
  else:
    print "Authenticated as {0}".format(di.user)

main.py

import di
import library

library.now()

di.user = "Fred"

library.now()

# $ python main.py
# Unauthenticated user
# Authenticated as Fred