Append 值或如果列表不存在则创建并插入？

Question

I found myself always writing this kind of ugly snippet when I have to insert a value to a non-existing list:

if hasattr(obj, 'key'):
    obj.key = []
obj.key.append(value)

Of course, I could use defaultdict(list) , but in this use-case I cannot do it a priori.

Is there a more pythonic yet simpler way of achieving this?

Answer 1

You could call setdefault on the instance dict, ie

vars(obj).setdefault('key', []).append(value)