two python lists dependency

Asked Jul 27 '23 at 10:12

Active Jul 27 '23 at 10:22

Viewed 27 times

Starting learning Python lists and stuck with the question

Simplifying I have a code:

A = []
B=[{'x':10},{'x':30}]
for elem in B:
       A.append(elem)     

for elem in B: ##changing B list
       elem['x']=elem['x']-1
print(A)

I've changed B list in the for cycle but last string output for A list is

[{'x': 9}, {'x': 29}]

So A list is affected too.

Could somebody explain why updating B list causes updating A list.

I expected A and B lists to be independent. Probably the answer is in append method documentation or area of elem visibility but cant find the exact answer

asked Jul 27 '23 at 10:12

PavelX

1

This is unrelated to lists, you are storing references to the same object. `elem` is not a copy of the `dict`s in your lists, it is a reference to them – UnholySheep Jul 27 '23 at 10:15
Got the idea, many thanks – PavelX Jul 27 '23 at 10:18
http://pythontutor.com can help understanding this kind of thing. – deceze Jul 27 '23 at 10:22

two python lists dependency

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