目录

1、浅拷贝和深拷贝2、直接赋值3、for循环4、切片5、copy()方法（1）list.copy()方法（2）copy.copy()方法6、deepcopy()方法

1、浅拷贝和深拷贝

浅拷贝复制指向某个对象的地址（指针），而不复制对象本身，新对象和原对象共享同一内存。

(相关资料图)

深拷贝会额外创建一个新的对象，新对象跟原对象并不共享内存，修改新对象不会影响到原对象。

赋值其实就是引用了原对象。两者指向同一内存，两个对象是联动的，无论哪个对象发生改变都会影响到另一个。

2、直接赋值

使用=来复制一个列表，实际上不仅复制了其中的内容，也复制了其内存地址，即引用了原列表。使用id()方法查看内存地址也是一样的。修改其中一个列表，也会直接更改另一个列表。

#!/usr/bin/env python
# -*- coding:utf-8 -*-
if __name__ == "__main__":
    a = ["a", ["b", "c", "d"], ["e", "f"]]
    # 直接复制，即引用列表
    b = a
    print(a)
    print(b)
    # 通过id()查看内存地址，为一样的
    print(id(a), id(b))
    b[0] = "g"
    b[1][0] = "f"
    print(a)
    print(b)

输出：

["a", ["b", "c", "d"], ["e", "f"]]
["a", ["b", "c", "d"], ["e", "f"]]
2030264836936 2030264836936
["g", ["f", "c", "d"], ["e", "f"]]
["g", ["f", "c", "d"], ["e", "f"]]

Process finished with exit code 0

3、for循环

使用for循环进行拷贝，仅第一层为深拷贝，对其它层依然是浅拷贝。

#!/usr/bin/env python
# -*- coding:utf-8 -*-
if __name__ == "__main__":
    a = ["a", ["b", "c", "d"], ["e", "f"]]
    b = []
    # 使用for循环进行拷贝，仅第一层为深拷贝
    for i in a:
        b.append(i)
    print(a)
    print(b)
    b[0] = "g"
    b[1][0] = "f"
    print(a)
    print(b)

输出：

["a", ["b", "c", "d"], ["e", "f"]]
["a", ["b", "c", "d"], ["e", "f"]]
["a", ["f", "c", "d"], ["e", "f"]]
["g", ["f", "c", "d"], ["e", "f"]]

Process finished with exit code 0

4、切片

使用切片方法进行拷贝，也仅对第一层为深拷贝，对其它层依然是浅拷贝。

#!/usr/bin/env python
# -*- coding:utf-8 -*-
if __name__ == "__main__":
    a = ["a", ["b", "c", "d"], ["e", "f"]]
    # 使用切片进行拷贝，仅第一层为深拷贝
    b = a[:]
    print(a)
    print(b)
    b[0] = "g"
    b[1][0] = "f"
    print(a)
    print(b)

输出：

["a", ["b", "c", "d"], ["e", "f"]]
["a", ["b", "c", "d"], ["e", "f"]]
["a", ["f", "c", "d"], ["e", "f"]]
["g", ["f", "c", "d"], ["e", "f"]]

Process finished with exit code 0

5、copy()方法

（1）list.copy()方法

使用list.copy()方法进行拷贝，也仅对第一层为深拷贝，对其它层依然是浅拷贝。由于列表中嵌套的列表实际保存的是地址，依然指向同一个内存地址。

#!/usr/bin/env python
# -*- coding:utf-8 -*-
 
if __name__ == "__main__":
    a = ["a", ["b", "c", "d"], ["e", "f"]]
    # 使用list.copy()方法进行拷贝，仅第一层为深拷贝
    b = a.copy()
    print(a)
    print(b)
    b[0] = "g"
    b[1][0] = "f"
    print(a)
    print(b)

输出：

["a", ["b", "c", "d"], ["e", "f"]]
["a", ["b", "c", "d"], ["e", "f"]]
["a", ["f", "c", "d"], ["e", "f"]]
["g", ["f", "c", "d"], ["e", "f"]]

Process finished with exit code 0

（2）copy.copy()方法

使用copy.copy()方法进行拷贝，也仅对第一层为深拷贝，对其它层依然是浅拷贝。

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import copy
 
if __name__ == "__main__":
    a = ["a", ["b", "c", "d"], ["e", "f"]]
    # 使用copy.copy()方法进行拷贝，仅第一层为深拷贝
    b = copy.copy(a)
    print(a)
    print(b)
    b[0] = "g"
    b[1][0] = "f"
    print(a)
    print(b)

输出：

["a", ["b", "c", "d"], ["e", "f"]]
["a", ["b", "c", "d"], ["e", "f"]]
["a", ["f", "c", "d"], ["e", "f"]]
["g", ["f", "c", "d"], ["e", "f"]]

Process finished with exit code 0

6、deepcopy()方法

使用copy.deepcopy()方法进行拷贝，对所有层均为深拷贝，改变新列表并不会影响到原列表，推荐使用。

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import copy
 
if __name__ == "__main__":
    a = ["a", ["b", "c", "d"], ["e", "f"]]
    # 使用copy.deepcopy()方法进行拷贝，对所有层均为深拷贝
    b = copy.deepcopy(a)
    print(a)
    print(b)
    b[0] = "g"
    b[1][0] = "f"
    print(a)
    print(b)

输出：

["a", ["b", "c", "d"], ["e", "f"]]
["a", ["b", "c", "d"], ["e", "f"]]
["a", ["b", "c", "d"], ["e", "f"]]
["g", ["f", "c", "d"], ["e", "f"]]

Process finished with exit code 0

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