Appending Lists, why is the output the way it is?

Question

Consider this code:
a, b = [0], [1]
a.append(b)
b.append(a)
print(a)
print(b)
# I expected an output like [0, [1]]
# [1, [0, [1]]]
# but it rather becomes an infinite list, can
# someone explain please?

Answer 1

🔹Because you've appended a pointer to that list, so when b changes the pointer sees the change. Same thing when a changes.
In your case result become infinite list...

👉 a.append(b) ⤵️
a is now [original_list_object_a,original_list_object_b].
So, when you change b, you change what a refers to.
...

🔹If you want to create a copy and therefore point to a different object, you can use next:

a, b = [0], [1]
a.append(b[:])
b.append(a[:])

print(a)
print(b)

Answer 2

@Khushal
Exactly! 👍
You're welcome 😉

Answer 3

Oh I think i get it somewhat, when we append b to a we are not appending the value of b but actually appending it's "address's value" so whenever b changes a changes too and this how it becomes an Infinite list. Thanks Lukar ToDo ! :)