Function to get user_id’s that had their opt-in status changed after processing of the change log

Given a list of users with their opt-in statuses and sequential change log of opt-in status updates that is applied to user list, I am trying to write a function to get a list of all user_ids (sorted by id) that had their opt-in status changed after processing of the change log

Sample Input:

        current_user_list: [
            User({
                id: 1,
                opted_in: false
            }),
            User({
                id: 19,
                opted_in: true
            }),
            User({
                id: 4,
                opted_in: true
            }),
            User({
                id: 54,
                opted_in: false
            })
        ]

        opt_in_change_log: [
            OptInChange({
                user_id: 19,
                action: 'opt_out'
            }),
            OptInChange({
                user_id: 1,
                action: 'opt_in'
            }),
            OptInChange({
                user_id: 71,
                action: 'opt_in'
            }),
            OptInChange({
                user_id: 19,
                action: 'opt_in'
            })
        ]

Sample Output

[ 1, 71 ]

My function takes two parameters, but I am not entirely sure how to extract user_id who had their opt-in changed

def find_users_with_opt_change(current_user_list, opt_in_change_log):

EDIT: users not stored in user list are considered opted_out

Answer

I would do it this way

def find_users_with_opt_change(current_user_list, opt_in_change_log):
    current_values = {}
    was_changed = []

    for i in current_user_list:
        current_values[i.id] = i.opted_in
    

    for change in opt_in_change_log:
        user_id = change.user_id
        current_value = current_values.get(user_id, False)

        if (current_value and change.action == 'opt_out') or (not(current_value) and change.action == 'opt_in'):
            current_values[user_id] = not(current_value)
            if user_id in was_changed:
                was_changed.remove(user_id)
            else:
                was_changed.append(user_id)
    
    return was_changed