安装插件：
pip install flask-uploads
创建上传文件对象：
from flask_uploads import UploadSet
#在这里限制允许上传类型
from flask_uploads import TEXT,IMAGES
uploads=UploadSet(“UPLOADS”,extensions=TEXT+IMAGES)
导出
from .ext_uploads import uploads
加载三方对象 在app.py
from exts import uploads
from flask_uploads import configure_uploa
