'Ask the tracking link to the service provider
:param pickings: A recordset of pickings
:return list: A list of string URLs, containing the tracking links for every picking'

def get_tracking_link(self, pickings):

    self.ensure_one()
    if hasattr(self, ('%s_get_tracking_link' % self.delivery_type)):
        return getattr(self, ('%s_get_tracking_link' % self.delivery_type))(pickings)
