'Return the item id for item_name (case-insensitive)'

@read_api
def get_item_id(self, field, item_name):

    rmap = {(icu_lower(v) if isinstance(v, unicode) else v): k for (k, v) in self.fields[field].table.id_map.iteritems()}
    return rmap.get((icu_lower(item_name) if isinstance(item_name, unicode) else item_name), None)
