Hello Tung,

There is also another option which is more flexible.
What you need is to prepare a users.csv 

You can use import via the odoo web service.
below the link to the quite old post - but the idea is pretty smart, I think, especially if you really want to have the control of your users, it's number and of course - data.
The example is about importing products, but it's just the switching of data model.

https://erpmoldeo.wordpress.com/2011/05/10/importing-products-with-web-services-in-openerp/

That's just a suggestion, which I would like you to know about :)

Maybe this help you at a certain moment.

WIsh you luck!

I once used code to create the users and restrict several parameters,and put them in the groups I wanted, but why do you want to create so many users anyway?

Here is an example of the code:

models.execute_kw(db, uid, password, 'res.users', 'create', [
    {'name': 'user_name',
     'login': 'user_email',  # Must be different each time 
     'password': 'user_password',
     'new_password': 'user_password',
     'sel_groups_1_9_10': 1,
     'sel_groups_20_21_22': 22,
     'sel_groups_35_36': 36,
     'sel_groups_49_50': 50,
     'sel_groups_2_3': 3,
     'sel_groups_26_28': 28,
     'sel_groups_44_45': 45,
     'notification_type': 'inbox',
     'tz': 'time_zone'}])