def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def __init__(
        self,
        new_item_default_value,
        min_size=0,
        max_size=None,
        item_spacing=ItemBox.ITEM_SPACING,
        max_width=None,
        max_height=None,
        *args,
        **kwargs):
    """
    Parameters: