how to add a portal role by python code
acl_users.portal_role_manager.addRole

portal._addRole(new_role)
try:
    acl_users.portal_role_manager.addRole(new_role)
except:
    pass

## Roles are store on __ac_roles__ attribute of object.
roles = list(portal.__ac_roles__)
roles += 'yournewrole'
portal.__ac_roles__ = tuple(roles)