I tried the following in the python interpreter:
>>> a = []
>>> b = {1:'one'}
>>> a.append(b)
>>> a
[{1: 'one'}]
>>> b[1] = 'ONE'
>>> a
[{1: 'ONE'}]
Here, after appending the dictionary b to the list a, I’m changing the value corresponding to the key 1 in dictionary b. Somehow this change gets reflected in the list too. When I append a dictionary to a list, am I not just appending the value of dictionary? It looks as if I have appended a pointer to the dictionary to the list and hence the changes to the dictionary are getting reflected in the list too.
I do not want the change to get reflected in the list. How do I do it?
Answers:
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Method 1
You are correct in that your list contains a reference to the original dictionary.
a.append(b.copy()) should do the trick.
Bear in mind that this makes a shallow copy. An alternative is to use copy.deepcopy(b), which makes a deep copy.
Method 2
Also with dict
a = []
b = {1:'one'}
a.append(dict(b))
print a
b[1]='iuqsdgf'
print a
result
[{1: 'one'}]
[{1: 'one'}]
Method 3
use copy and deep copy
All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0