在python中的字典的深拷贝

Question

我想dict在python中制作一个深层副本.不幸的是,该.deepcopy()方法不存在dict.我怎么做？

>>> my_dict = {'a': [1, 2, 3], 'b': [4, 5, 6]}
>>> my_copy = my_dict.deepcopy()
Traceback (most recent calll last):
  File "<stdin>", line 1, in <module>
AttributeError: 'dict' object has no attribute 'deepcopy'
>>> my_copy = my_dict.copy()
>>> my_dict['a'][2] = 7
>>> my_copy['a'][2]
7

最后一行应该是3.

我希望这些修改my_dict不会影响快照my_copy.

我怎么做？该解决方案应与Python 3.x兼容.

Answer 1

怎么样:

import copy
d = { ... }
d2 = copy.deepcopy(d)

Python 2或3:

Python 3.2 (r32:88445, Feb 20 2011, 21:30:00) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import copy
>>> my_dict = {'a': [1, 2, 3], 'b': [4, 5, 6]}
>>> my_copy = copy.deepcopy(my_dict)
>>> my_dict['a'][2] = 7
>>> my_copy['a'][2]
3
>>>

Answer 2

dict.copy()是一个浅复制函数,用于字典
id是内置函数,它为您提供变量的地址

首先,您需要了解"为什么会出现这个特殊问题？"

In [1]: my_dict = {'a': [1, 2, 3], 'b': [4, 5, 6]}

In [2]: my_copy = my_dict.copy()

In [3]: id(my_dict)
Out[3]: 140190444167808

In [4]: id(my_copy)
Out[4]: 140190444170328

In [5]: id(my_copy['a'])
Out[5]: 140190444024104

In [6]: id(my_dict['a'])
Out[6]: 140190444024104

键'a'的两个词组中出现的列表的地址指向相同的位置.
因此,当您更改my_dict中列表的值时,my_copy中的列表也会更改.

解:

In [7]: my_copy = {key: value[:] for key, value in my_dict.items()}

In [8]: id(my_copy['a'])
Out[8]: 140190444024176

或者您可以使用上面提到的深度复制.

Answer 3

Python 3.x

从复制导入deepcopy

my_dict = {'one': 1, 'two': 2}
new_dict_deepcopy = deepcopy(my_dict)

没有深度复制,我无法从我的域字典中删除主机名字典.

没有深度复制我收到以下错误:

"RuntimeError: dictionary changed size during iteration"

...当我尝试从另一个字典里面的字典中删除所需的元素时.

import socket
import xml.etree.ElementTree as ET
from copy import deepcopy

domain是一个字典对象

def remove_hostname(domain, hostname):
    domain_copy = deepcopy(domain)
    for domains, hosts in domain_copy.items():
        for host, port in hosts.items():
           if host == hostname:
                del domain[domains][host]
    return domain

示例输出:[ orginal ] domains = {'localdomain':{'localhost':{'all':'4000'}}}

[new] domains = {'localdomain':{}}}

所以这里发生的事情是我正在迭代字典的副本而不是遍历字典本身.使用此方法,您可以根据需要删除元素.