There is not a good reason to use _ in the scripts. While using from interactive interpretor if you are doing any mathematical calculation, and you want the the result of the previous expression, you can use _. Python tutorial introduces the _ in the very same context. I see that the behavior is carried over from certain shell behaviors.
In your example:
_, x = L.pop()
would fail because L.pop() would return a single value and you cannot assign it to two variables and also it not a good idea to assign values to _ which has a special meaning.
