解决方法

首先安装django-extensions：

pip install django-extensions

然后把django-extensions加入到setting.py文件下的INSTALLED_APPS中：

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    "device_discover",
    "django_crontab",
    "django_extensions", # 嗷嗷嗷
    
]

最后就可以用

python manage.py clear_cache --all

显示：Cache "default" has been cleared!就Ok啦