"""list_basics.py - Python 列表基础示例

包含常见的列表操作示例：创建、访问、切片、增删、查询、排序、复制、遍历、推导式等。
运行后会打印每个示例的结果（并在代码中注释预期输出）。
"""

import copy

def main():
    skills = ["python", "java", "c++", "c#", "javascript"]

    print("原始列表:", skills)
    # 访问与切片
    print("skills[0] ->", skills[0])           # python
    print("skills[-1] ->", skills[-1])         # javascript
    print("skills[1:4] ->", skills[1:4])       # ['java', 'c++', 'c#']
    print("skills[-2:] ->", skills[-2:])       # ['c#', 'javascript']
    print("skills[::-1] ->", skills[::-1])     # 反转，返回新列表

    # 增加
    skills.append("go")
    print("append ->", skills)                 # 尾部添加

    skills.extend(["rust", "swift"])
    print("extend ->", skills)                 # 尾部添加多个

    skills.insert(1, "typescript")
    print("insert ->", skills)                 # 在索引1前插入

    # 删除
    skills.remove("java")               # 删除第一个 'java'
    print("remove('java') ->", skills)

    popped = skills.pop()                      # 弹出最后一个
    print("pop() ->", popped, "; after pop ->", skills)

    popped_idx = skills.pop(2)                 # 弹出索引2的元素
    print("pop(2) ->", popped_idx, "; after pop ->", skills)

    # 查询
    print("'python' in skills ->", 'python' in skills)
    print("skills.count('python') ->", skills.count('python'))

    # 排序与反转
    nums = [3, 1, 4, 1, 5]
    print("nums before:", nums)
    print("sorted(nums) ->", sorted(nums))     # 返回新列表
    nums.sort()
    print("nums after sort() ->", nums)        # 原地排序
    nums.reverse()
    print("nums after reverse() ->", nums)     # 原地反转

    # 复制与可变性
    a = [1, 2, [3, 4]]
    b = a          # b 与 a 指向同一个对象
    c = a[:]       # 浅拷贝，顶层复制
    d = copy.deepcopy(a)  # 深拷贝

    a[0] = 100
    a[2].append(5)
    print("a:", a)
    print("b (same ref):", b)    # 反映 a 的所有变化
    print("c (shallow copy):", c) # c[0] 未改变，但 c[2]（嵌套列表）受影响
    print("d (deep copy):", d)    # 完全独立

    # 遍历与推导式
    for i, val in enumerate(['a', 'b', 'c']):
        print("enumerate:", i, val)

    squares = [x*x for x in range(6) if x % 2 == 0]
    print("squares (comprehension):", squares)

    # 例：交换两个元素
    arr = [1, 2, 3]
    arr[0], arr[2] = arr[2], arr[0]
    print("swap arr ->", arr)

    # 解包（剩余收集）
    first, *middle, last = [10, 20, 30, 40, 50]
    print("unpack ->", first, middle, last)


if __name__ == '__main__':
    main()