python: Appending a dictionary to a list - I see a pointer like behavior

Question

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 'a'. 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?

Thank you for your time!

Answer 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.

Answer 2

Also with dict

a = [] b = {1:'one'}  a.append(dict(b)) print a b[1]='iuqsdgf' print a 

result

[{1: 'one'}] [{1: 'one'}]