Python：AttributeError：'NoneType'对象没有属性'append'

Question

我的程序看起来像

# global
item_to_bucket_list_map = {}

def fill_item_bucket_map(items, buckets):
    global item_to_bucket_list_map

    for i in range(1, items + 1):
        j = 1
        while i * j <= buckets:
            if j == 1:
                item_to_bucket_list_map[i] = [j]
            else:
                item_to_bucket_list_map[i] = (item_to_bucket_list_map.get(i)).append(j)
            j += 1
        print "Item=%s, bucket=%s" % (i, item_to_bucket_list_map.get(i))


if __name__ == "__main__":
    buckets = 100
    items = 100
    fill_item_bucket_map(items, buckets)

当我运行它时，它会抛出我

AttributeError: 'NoneType' object has no attribute 'append'

不知道为什么会这样？当我已经在每个列表的开头创建列表时j

Answer 1

实际上，您存储None在此处： append()更改列表并返回None

 item_to_bucket_list_map[i] = (item_to_bucket_list_map.get(i)).append(j)

例：

In [42]: lis = [1,2,3]

In [43]: print lis.append(4)
None

In [44]: lis
Out[44]: [1, 2, 3, 4]