[Mailman-Developers] Unclear usage of `member = ISubscriptionManager(mlist).register(…)`

Hello,

I am trying to understand the source code. My reading is, that interfaces/subscriptions.py:class ISubscriptionManager.register always returns a 3-tuple and the last element of the tuple is a member object, or None. This coincides with the implementation in app/subscriptions.py.SubscriptionManager.register . cli_synmembers.py:add_members() contains:

member = registrar.register(
    subscriber,
    pre_verified=True,
    pre_approved=True,
    pre_confirmed=True,
    send_welcome_message=welcome_msg)[2]
member.preferences.delivery_status = delivery_status
member.preferences.delivery_mode = delivery_mode
return

and commands/cli_addmembers.py:add_members() contains

member = registrar.register(
    subscriber,
    pre_verified=True,
    pre_approved=True,
    pre_confirmed=True,
    invitation=invite,
    send_welcome_message=welcome_msg)[2]
if member is not None:
    member.preferences.delivery_status = delivery_status
    member.preferences.delivery_mode = delivery_mode
return

So my question is: when regirstar.register returns a tuple, the last argument of which is a members, why do the above snippets store the result in a variable called member?

How are the set preferences set to member handled further, as my reading is that the variable just disappears, immediately after member.preferences is set?

Greeting Дилян