Python中copy.copy与copy.deepcopy的区别及用法

# 示例代码：直接赋值的行为
a = [10, [20, 30]]
b = a

print(f"a 的内存地址: {id(a)}")
print(f"b 的内存地址: {id(b)}")
print(f"a 与 b 是否为同一对象: {a is b}")

# 修改 b 的第 0 个元素
b[0] = 99
print(f"修改 b[0] 后，a 的值为: {a}")

import copy

# 内部全为不可变类型
original = [1, 2, "hello", (3, 4)]
copied = copy.copy(original)

copied[0] = 100
copied[2] = "world"

print(f"原列表 original: {original}")
print(f"副本 copied:     {copied}")
print(f"外层容器地址对比: id(original)={id(original)}, id(copied)={id(copied)}")

import copy

# 包含嵌套子列表
source = ["北京", ["海淀", "朝阳"]]
shallow = copy.copy(source)

# 仅修改外层元素，互不干扰
shallow[0] = "上海"

# 修改嵌套的可变子列表，产生连锁影响！
shallow[1].append("昌平")

print(f"原数据 source:  {source}")
print(f"副本 shallow:   {shallow}")
print(f"嵌套列表内存地址比对: {id(source[1]) == id(shallow[1])}")

import copy

source = ["北京", ["海淀", "朝阳"]]
deep = copy.deepcopy(source)

# 对深拷贝对象的内层与外层进行全面修改
deep[0] = "广州"
deep[1].append("天河")

print(f"原数据 source: {source}")
print(f"副本 deep:    {deep}")
print(f"内层列表是否为同一对象: {source[1] is deep[1]}")

import copy

# 构建一个自引用的列表结构
loop_list = [1, 2]
loop_list.append(loop_list)  # 列表第三个元素指向自身

# 执行深拷贝
cloned = copy.deepcopy(loop_list)

print(f"原列表 loop_list 长度: {len(loop_list)}")
print(f"克隆后 cloned 长度:   {len(cloned)}")
print(f"克隆列表的自引用是否指向新列表本身: {cloned[2] is cloned}")
print(f"克隆列表的自引用是否脱离了原列表:   {cloned[2] is not loop_list}")

import copy

class TaskSession:
    def __init__(self, name, tasks, shared_channel=None):
        self.name = name
        self.tasks = tasks  # 可变任务列表
        self.shared_channel = shared_channel  # 系统通信信道（不应深拷贝）

    def __copy__(self):
        # 自定义浅拷贝：直接传入属性原引用构造新实例
        return TaskSession(self.name, self.tasks, self.shared_channel)

    def __deepcopy__(self, memo):
        # 必须接收 memo 字典并在调用子属性 deepcopy 时显式透传
        cls = self.__class__
        new_instance = cls.__new__(cls)
        # 提前登记 memo，防止复合属性内部产生相互引用导致环路
        memo[id(self)] = new_instance
        
        # 逐属性定制深拷贝规则
        for k, v in self.__dict__.items():
            if k == "shared_channel":
                # 保持通信信道单例共享
                setattr(new_instance, k, self.shared_channel)
            else:
                setattr(new_instance, k, copy.deepcopy(v, memo))
                
        return new_instance

session = TaskSession("Worker-1", ["task_a", "task_b"], shared_channel="SOCKET_001")
cloned_session = copy.deepcopy(session)
cloned_session.tasks.append("task_c")

print(f"原 session 任务列表: {session.tasks}")
print(f"副本 session 任务列表: {cloned_session.tasks}")
print(f"通信信道是否共享: {session.shared_channel is cloned_session.shared_channel}")

import copy
import time

data = list(range(100000))

t0 = time.perf_counter()
shallow_copy = copy.copy(data)
t1 = time.perf_counter()
deep_copy = copy.deepcopy(data)
t2 = time.perf_counter()

print(f"copy.copy 耗时:     {(t1 - t0) * 1000:.3f} ms")
print(f"copy.deepcopy 耗时: {(t2 - t1) * 1000:.3f} ms")
print(f"深拷贝相对浅拷贝倍率: {((t2 - t1) / (t1 - t0)):.1f} 倍")