Here is example of adding the admin user to the group you have created trough the XML:

        <record model="res.groups" id="salesmen_commission_group">
            <field name="name">Commission</field>
            <field name="comment">Salesmen Commission Permission Group.</field>
            <field name="category_id" ref="module_category_commission"/>
            <field name="users" eval="[(4, ref('base.user_root'))]"/>
        </record>

Hi dude,

You can try with this for python

def set_commission_group(self, user_id):
    commission_group = self.env.ref('your_module_name.salesmen_commission_group')
    commission_group.write({'users': [(4, user_id)]})

Hi, Carefull with this action you will reset the group members with users items

instead we can can just add on remove a user with + and -
usersToAdd = searching user with domain or somthing
group = env['res.groups'].search([('id', '=', GROUP_ID)])
group.write({'users' : group.users + usersToAdd})
or
group.write({'users' : group.users - usersToAdd})

If you were trying to add user into an existing group with noupdate on, this might be the best and only way for you to add user into the group

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <data>
        <record id="base.user_admin" model="res.users">
            <field name="groups_id" eval="[(4, ref('account.group_account_user'))]"/>
        </record>
    </data>
</odoo>

Hi,

in my case it worked in the following way

@api.multi
def assign_perms(self):
    users_id = [1, 2, 3, 4, 5, .........]
    aux_users = [(4, i) for i in users_id]
    group = self.env['res.groups'].search([('id', '=', self.env.ref('module_name.identifier').id)])
    group.write({'users': aux_users})