How to slice (in Python) “all but the last n” item

问题:

This question already has an answer here:

• List slicing with dynamic index on [:index] 4 answers

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])