I guess you are using Python. It's hard to help without knowing what you are doing, but at some moment you are trying to access a value with an out of range index. The interpreter helps you giving you the line of your code that produces the error. You need to control that part of your code.

when testing, only one case alert that "IndexError: list index out of range". I can't figure out why it occurs.My logic of the problem, circulating the list, judging each neighbours, set a empty list which same size with the test one, change newlist's number. This works in three cases,except glider. Says the newlist list index out of range. could anyone give me a hand?