即使在输入 if -else 的 else 之后，return 语句在 Python 中也不起作用？

Question

def quickSort(nums,start,end):    
    if(start < end):
        Pindex =partition(nums,start,end)
        quickSort(nums,start,Pindex-1)
        quickSort(nums,Pindex+1,end)   
    else:
        print("Else",start,end,nums)
        return nums;

The return statement is not executed even if the print ("Else",start,end,nums0 is executed

Answer 1

The problem is that you are ignoring the return values from your recursive quickSort calls (which, by the way, is conventionally spelled quicksort ).

So even though your base case (the else ) returns a value, it will subsequently be discarded.

You need to handle the return values of both recursive quicksort calls:

1. the first result needs to be assigned to a variable which you subsequently use for the next quicksort call
2. the second result needs to be returned

Adjusting the code, and fixing the formatting, we get:

def quicksort(nums, start, end):
    if start < end:
        pindex = partition(nums, start, end)
        nums = quicksort(nums, start, pindex - 1)
        return quicksort(nums, pindex + 1, end)
    else:
        return nums

Furthermore, it is conventional to handle the base case of a recursion first , because then we don't need to indent as much (since we also don't need the else ):

def quicksort(nums, start, end):
    if start >= end:
        return nums

    pindex = partition(nums, start, end)
    nums = quicksort(nums, start, pindex - 1)
    return quicksort(nums, pindex + 1, end)