Unknown Python Bug

Question

I am trying to implement a code for solving tower of hanoi. So far i have implemented just the functions for moving the disks.However i have encoutered a bug. Here's the code
https://code.sololearn.com/cwGYE3i7v3TZ/?ref=app
The code ouputs:
[[1, 2, 3], [None, None, None], [None, None, None]]
[[None, 2, 3], [None, None, 1], [None, None, 1]]
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I can't figure out how does disk1 reaches here (tower2 )when i have coded it to place the disk in tower 3.
I have tried some other methods but all of them lead to this
I am using python3 and this bug appears on all my devices.

Answer 1

The error is in line 3. towers=3*[len(disks)*[None]] creates three instances of the same list. If you change one of them, you change all of them. You can create three independent lists with towers = [len(disks)*[None] for i in range(3)]

Answer 2

thank you