问未定义Python名称'os‘

EN

from settings import PROJECT_ROOT

DEBUG = True
TEMPLATE_DEBUG = DEBUG


DATABASES = {
    'default': {
        'ENGINE':  'django.db.backends.sqlite3',
        'NAME' : os.path.join(BASE_DIR, 'db_name.sqlite3'),
    }
}


# Make this unique, and don't share it with anybody.
SECRET_KEY = 'sdfgtardyure34654356435'

# Python dotted path to the WSGI application used by Django's runserver; added in v1.4
WSGI_APPLICATION = 'wsgi.application'

############### PYSEC specific variables

# assumes this directory exists
DATA_DIR = "%s/pysec/data/" % PROJECT_ROOT

Traceback (most recent call last):
  File "C:\Python27\pysec-master\local_settings-example.py", line 11, in <module>
    'NAME' : os.path.join(BASE_DIR, 'db_name.sqlite3'),
NameError: name 'os' is not defined