def _get_stat_ops(nodes):
return set(node for node in iter_nodes(nodes)
if isinstance(node.op, StatOperator))
def _input_columns(self):
input_nodes = set(node for node in iter_nodes([self.column_group])
if not node.parents)
return list(
set(col for node in input_nodes for col in node.flattened_columns))
