Python3.x 为什么空列表也能起作用

您第二次调用selection_sort实际上会返回一个空列表，这就是为什么binary_search会得到一个空列表.

原因是这一行:

sorted_nums.append(nums.pop(smallest_index))

在你的selection_sort routine 中，你从nums开始的所有值都是pop.这是清空(并覆盖)输入列表nums

您可以通过制作nums的浅表副本来避免这种情况:

from typing import List


def binary_search(nums: List[int], item: int):
    print("binary_search nums", nums)
    low = 0
    high = len(nums) - 1

    while low <= high:
        middle = (low + high) // 2

        if nums[middle] == item:
            return middle
        if nums[middle] > item:
            high = middle - 1
        if nums[middle] < item:
            low = middle + 1
    return None


def smallest_find(nums: List[int]):
    smallest = nums[0]
    smallest_index = 0

    for i in range(1, len(nums)):
        if nums[i] < smallest:
            smallest = nums[i]
            smallest_index = i
    return smallest_index


def selection_sort(nums: List[int]):
    sorted_nums = []
    nums_ = nums[:] # shallow copy
    for _ in range(len(nums_)):
        smallest_index = smallest_find(nums_)
        sorted_nums.append(nums_.pop(smallest_index))
    return sorted_nums

import random

while True:
    nums = [random.randint(-100, 100) for _ in range(20)]
    item = 24
    if item in nums:
        print(nums)
        print(selection_sort(nums))
        print(binary_search(selection_sort(nums), item))
        break

输出:

[41, -59, 38, -50, 25, -62, 58, -81, 7, 24, -93, 41, 92, 3, 65, -61, 47, -54, 72, 65]
[-93, -81, -62, -61, -59, -54, -50, 3, 7, 24, 25, 38, 41, 41, 47, 58, 65, 65, 72, 92]
binary_search nums [-93, -81, -62, -61, -59, -54, -50, 3, 7, 24, 25, 38, 41, 41, 47, 58, 65, 65, 72, 92]
9