list syntax

[buran]

>>> x = [1,2,3]
>>> y = x
>>> z = x[::]
>>> x
[1, 2, 3]
>>> y
[1, 2, 3]
>>> z
[1, 2, 3]
>>> x[0] = 4
>>> x
[4, 2, 3]
>>> y
[4, 2, 3]
>>> z
[1, 2, 3]
>>> id(x)
140222264135304
>>> id(y)
140222264135304
>>> id(z)
140222264168648

in your example y = x does not create new list, y reference the same object as x. In my example you can see they have the same id (i.e. they are the same object). I showed one of the possible methods to copy/clone a list. There are also other options see https://stackoverflow.com/a/2612815/4046632