python Dictionary Mutable Clarification

Question

I am using dictionary as argument to the function.

When i Change the values of the argument passed, it getting changed parent dictionary.i have used dict.copy() but still not effective.

How to avoid mutable in dictionary values. Need your inputs

>>> myDict = {'one': ['1', '2', '3']}
>>> def dictionary(dict1):
    dict2 = dict1.copy()
    dict2['one'][0] = 'one'
    print dict2


>>> dictionary(myDict)
{'one': ['one', '2', '3']}
>>> myDict
{'one': ['one', '2', '3']}

My intention was my parent dictionary should be changed. Thanks, Vignesh

http://stackoverflow.com/questions/2465921/how-to-copy-a-dictionary-and-only-edit-the-copy — jkr, Dec 04 '16 at 08:13
"My intention was my parent dictionary should be changed." That is what is happening. Did you mean to say your intention is that it should *not* be changed? — BrenBarn, Dec 04 '16 at 08:15

score 4 · Accepted Answer · edited Dec 04 '16 at 08:24

Use deepcopy() from the copy module.

from copy import deepcopy
myDict = {'one': ['1', '2', '3']}
def dictionary(dict1):
    dict2 = deepcopy(dict1)
    dict2['one'][0] = 'one'
    print dict2

See the docs:

A shallow copy constructs a new compound object and then (to the extent possible) inserts references into it to the objects found in the original.
A deep copy constructs a new compound object and then, recursively, inserts copies into it of the objects found in the original.

score 1 · Answer 2 · answered Dec 04 '16 at 08:17

You can use deepcopy from copy module like this example:

from copy import deepcopy

myDict = {'one': ['1', '2', '3']}

def dictionary(dict1):
    dict2 = deepcopy(dict1)
    dict2['one'][0] = 'one'
    print  dict2

dictionary(myDict)
print(myDict)

Output:

dict2 {'one': ['one', '2', '3']}
myDict {'one': ['1', '2', '3']}

python Dictionary Mutable Clarification

2 Answers2