当 n 可能为零时，如何切片（在 Python 中）“除最后 n”之外的所有项目？
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How to slice (in Python) "all but the last n" items when n may be zero?
提问by workerjoe
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:
我在 Python 中有一个项目列表，我需要获取“除最后 N 个之外的所有”项目。当 N 为零（在这种情况下我想要整个列表）并且当 N 大于或等于列表的长度（在这种情况下我想要一个空列表）时，它需要工作。这在大多数情况下有效：
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?
但它在 N 为零的情况下失败。 mylist[:0]返回一个空列表：[]。是否有一个 Python 切片符号可以做我想要的，或者一个简单的函数？
采纳答案by John La Rooy
You can pass Noneto the slice
你可以传递None给切片
print(mylist[:-n or None])
