How do I check if the python debug option is set from within a script

If I'm in debug mode, I want to do other stuff than when I'm not.

if DEBUG:
    STORED_DATA_FILE = os.path.join(TEMP_DIR, 'store.dat')
    LOG_LEVEL = logging.DEBUG
    print "debug mode"
else:
    STORED_DATA_FILE = os.path.join(SCRIPT_PATH, 'store.dat')
    LOG_LEVEL = logging.INFO
    print "not debug mode"

then:

python script.py
not debug mode

python -d script.py
debug mode

How can I detect that? It certainly isn't using the __debug__ variable.