python-3.x - 在类中声明二维数组时出现名称错误

Question

我是 Python 新手，我正在尝试制作一个包含 2D 数组作为棋盘的游戏。我之前寻找过如何从 StackOverflow 声明 2D 数组，但由于某种原因，我得到一个NameErrorcols 未定义。我在做什么错？

class HelloWorld:
    rows = 5
    cols = 5
    arr = [[0 for i in range(cols)] for j in range(rows)]

编辑：这是回溯：

Traceback (most recent call last):
  File "c:/Users/MyName/Documents/Python Scripts/HelloWorld.py", line 1, in <module>
    class HelloWorld:
  File "c:/Users/MyName/Documents/Python Scripts/HelloWorld.py", line 4, in HelloWorld
    arr = [[0 for i in range(cols)] for j in range(rows)]
  File "c:/Users/MyName/Documents/Python Scripts/HelloWorld.py", line 4, in <listcomp>
    arr = [[0 for i in range(cols)] for j in range(rows)]
NameError: name 'cols' is not defined