Sorry if this is an old issue. (I searched but didn't find it.) I can create a new user this way:

new_user = server.users.add(name, siteRole)

The add function has this signature:

def add(self, user_item)

The UserItem constructor explicitly sets the password property like this:

def __init__(self, name, site_role, auth_setting=None):
        self._auth_setting = None
        self._domain_name = None
        self._external_auth_user_id = None
        self._id = None
        self._last_login = None
        self._name = None
        self._site_role = None
        self._workbooks = None
        self.email = None
        self.fullname = None
        self.password = None

And as near as I can tell (??) there is no setter in the UserItem class for a password property.

I tried doing this, which does compile and run:

new_user.password = args.newpassword
print("\nPassword changed to {0}".format(new_user.password))
new_user = server.users.update(new_user)

The server.users.update(new_user) call did result in a PUT request, but per Fiddler, the PUT request had only this in it (no password):

<tsRequest><user authSetting="ServerDefault" siteRole="SiteAdministrator" /></tsRequest>

In the UserRequest class (request_factory.py), there's a definition for an update_req method that would seem to take a password:

def update_req(self, user_item, password=''):
...
    if password:
        user_element.attrib['password'] = password

But I can't tell how to reach this method directly. So I'm stuck with being able to create a user but not assign a password. (And can't sign in as that user.)