The exception is right there. It's an index error, that is it's trying to do something going beyond the range of what this thing could deal with.

但他事实上抛出一个异常，异常就在这里，这是一个下标错误,它是试图去取超出范围的元素造成的。

麻省理工公开课 - 计算机科学及编程导论课程节选

Before I type in that expression, I get an error, right?

在我输入表达式之前，出现一个错误，对吧？

麻省理工公开课 - 计算机科学及编程导论课程节选