"TypeError:“生成器"对象不可下标"当我尝试使用for循环处理二维列表时 [英] "TypeError: 'generator' object is not subscriptable" when I try to deal with 2-dimensional list with for-loop

问题描述

class test(object):
    def __init__(self, name):
        self.name = ''


testList = [(test("empty") for i in range(3)) for j in range(2)]


for m in range(3):
    for n in range(2):

        testList[m][n].name = "changed"

我正在尝试检查和更改仅包含对象的二维列表中的项目.我先建立了2d列表，然后尝试使用double for循环影响其中的项目，但它返回TypeError.

I'm trying to check and change items of a 2-dimensional list which contains objects only. I built 2d list first and tried to affect the items in it with double for-loop but it returns TypeError.

Traceback (most recent call last):
  File "test.py", line 12, in <module>
    testList[m][n].name = "changed"
TypeError: 'generator' object is not subscriptable

我真的不明白这里发生了什么，因为它看起来很简单而且可行.该脚本无法与 testList [0] [0] .name ="changed" (而不是 testList [m] [n] )一起运行，因此我怀疑该循环不允许这样运行.但是为什么呢?

I really couldn't understand what's going on here as it seems quite simple and viable. The script could not run with testList[0][0].name = "changed" (instead of testList[m][n]) so I suspect that the loop is not allowed to run like this. But why?

推荐答案

您没有创建列表列表，而是创建了生成器对象列表.这些生成器对象处于休眠状态，直到代码对其进行迭代之前它们才处于活动状态.即使那样，您也没有 序列 ，这是使用索引所必需的.为了能够分配给索引，您需要一个 mutable 序列.

You didn't create a list of lists, you created a list of generator objects. Those generator objects are lying dormant, they are not active until code iterates over them. Even then, you don't have a sequence, which is what is required to use indexing. To be able to assign to indexes you need a mutable sequence.

如果要使每个嵌套索引可变，则必须生成列表，而不是生成器.将(...)括号替换为 [...] 方括号以创建列表理解:

If you want to make each nested index mutable, you have to generate lists, not generators. Replace the (...) parentheses with [...] square brackets to create a list comprehension instead:

testList = [[test("empty") for i in range(3)] for j in range(2)]

立即执行列表推导，然后生成一个列表对象.列表是可变序列.

List comprehensions are executed immediately, there and then, producing a list object. Lists are mutable sequences.

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