问题
I have a list of items in Python and I need to get "all but the last N" items. It needs to work when N is zero (in which case I want the whole list) and when N is greater than or equal to the length of the list (in which case I want an empty list). This works in most cases:
mylist=[0,1,2,3,4,5,6,7,8,9]
print( mylist[:-n] )
But it fails in the case where N is zero. mylist[:0] returns an empty list: []. Is there a Python slicing notation that will do what I want, or a simple function?
回答1:
You can pass None to the slice
print(mylist[:-n or None])
来源：https://stackoverflow.com/questions/30765493/how-to-slice-in-python-all-but-the-last-n-items-when-n-may-be-zero