Managing users in _users with couchdb-python

I'm trying to store and retrieve user from the database _users using couchdb-python. I'm a beginner here with couchdb.

I mapped the python class User with couchdb Document couchdb.mapping.Document like this:

import couchdb.mapping as cmap


class User(cmap.Document):
    name = cmap.TextField()
    password = cmap.TextField()
    type = 'user'
    roles = {}

but this is not working. I got doc.type must be user ServerError so probably the way I'm declaring the type is not correct.

How should I construct my class to be used with the _users database?