odoo_server-action_subscribe-newsletter.py

target_list_id = 6 # "[FR] Newsletter"

for rec in records: # contacts on which to work (user selection)
  existing_contacts = env['mailing.contact'].search([('email', '=', rec.email)])
  if len(existing_contacts) > 1:
    raise UserError(rec.name + " has multiple entries in the mailing contacts.\nPlease clean things up and get back here after having removed the duplicates.")
  elif len(existing_contacts) == 1:
    for recipient in existing_contacts: # should get exactly 1 recipient
      list_ids = [listid.id for listid in recipient.list_ids] # get all the lists the user is subscribed to
      if target_list_id in list_ids:
        raise UserError(rec.name + " (" + rec.email + ") already receives the newsletter.")
      else:
        recipient.write({ # add the newsletter to the list of subscription
          'list_ids': [ tuple(list_ids) + (target_list_id,) ]
        })
  elif rec.email:
    env['mailing.contact'].create({
      'name': rec.name,
      'email': rec.email,
      'company_name': rec.parent_id.name,
      'country_id': rec.country_id.id,
      'list_ids': [(target_list_id)]
    })
  # else: no email address provided -> discard!