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

My program looks like

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)

When I run this, it throws me

当我跑的时候，它把我甩了

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

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

Not sure why this would happen? When I am already creating a list at start of each j

不知道为什么会这样?当我已经在每个j的开头创建一个列表时

2 个解决方案

#1

Actually you stored None here: append() changes the list in place and returns None

实际上，您在这里存储了None: append()更改了列表的位置，并返回None

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

example:

例子:

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

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

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

#2

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

The while loop, however, can be simplified to

然而，while循环可以简化为

    for j in range(1, buckets / i + 1): # + 1 due to the <=
        if j == 1:
            mylist = []
        else:
            mylist = item_to_bucket_list_map.get(i)
        mylist.append(j)
        item_to_bucket_list_map[i] = mylist

#1