Deep copy of a dict in python Deep copy of a dict in python python python

Deep copy of a dict in python

How about:

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

Python 2 or 3:

Python 3.2 (r32:88445, Feb 20 2011, 21:30:00) [MSC v.1500 64 bit (AMD64)] on win32Type "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>>>

dict.copy() is a shallow copy function for dictionary
id is built-in function that gives you the address of variable

First you need to understand "why is this particular problem is happening?"

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]: 140190444167808In [4]: id(my_copy)Out[4]: 140190444170328In [5]: id(my_copy['a'])Out[5]: 140190444024104In [6]: id(my_dict['a'])Out[6]: 140190444024104

The address of the list present in both the dicts for key 'a' is pointing to same location.
Therefore when you change value of the list in my_dict, the list in my_copy changes as well.

Solution for data structure mentioned in the question:

In [7]: my_copy = {key: value[:] for key, value in my_dict.items()}In [8]: id(my_copy['a'])Out[8]: 140190444024176

Or you can use deepcopy as mentioned above.

Python 3.x

from copy import deepcopy

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

Without deepcopy, I am unable to remove the hostname dictionary from within my domain dictionary.

Without deepcopy I get the following error:

"RuntimeError: dictionary changed size during iteration"

...when I try to remove the desired element from my dictionary inside of another dictionary.

import socketimport xml.etree.ElementTree as ETfrom copy import deepcopy

domain is a dictionary object

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

Example output:[orginal]domains = {'localdomain': {'localhost': {'all': '4000'}}}

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

So what's going on here is I am iterating over a copy of a dictionary rather than iterating over the dictionary itself. With this method, you are able to remove elements as needed.