code: def list_from_env(key, default=""):
      
      try:
          val = os.environ.get(key, default)
          return val.split(',')
      except (KeyError, ValueError):
          return []
docs: Splits a string in the format "a,b,c,d,e,f" into
      ['a', 'b', 'c', 'd', 'e', 'f', ]