In python, what happens when two lists are set as equal and you change one? Spoiler: both change. Why?

Question

I was stumped by this question in a challenge. Please help me understand how this works. I do not understand why 'a' is changed when 'b' is changed.

# Orignal code by Nabeel Gm

a=[2,4,6,8]
b=a
b[0]=7
# a=[7,4,6,8]
# b=[7,4,6,8]
a[3]=9
# a=[7,4,6,9]
# b=[7,4,6,9]
b.append(5)
# a=[7,4,6,9,5]
# b=[7,4,6,9,5]
print(a)
print(b)
# I would expect:
# a=[2,4,6,9]
# b=[7,4,6,8,5]

Answer 1

If you have a list a, and assign b to a [b=a],b will point to the object a's value/address which is a list. Any changes made in b will occur to a because they refer to the same address that store's a list.

You have to assign a copy of a to b to avoid this.
[b=a.copy()]

Answer 2

Yep. When you do

b = a

b is literally object a, b is merely an alias of a. You might want to read on shallow copy vs deep copy.

https://realpython.com/copying-JUMP_LINK__&&__python__&&__JUMP_LINK-objects/

Answer 3

Brian M. Warner If you use the id() method you'll see that both a and b point to the same object.
id(a) == id(b)
>>>True

Answer 4

Thank you! Is there a way to check or refer to this address or find the aliases?

Answer 5

I don't know,

I saw this for the first time, but Astralis' answer was so good that I learned to know

Thank you very much

Answer 6

Check this out https://youtu.be/TMWqVBmv-cc

Answer 7

when a is equal to b, and you change a, b must be changed