python安装gridfs模块的命令是怎么写的

我输入命令:
pip install gridfs
提示:
Could not find any downloads that satisfy the requirement gridfs
No distributions at all found for gridfs

装mongodb，它属于一个模块

http://stackoverflow.com/questions/24101300/pip-could-not-find-any-downloads-that-satisfy-the-requirement-sqlalchemy