[Python] Reference list object by a variable is different than for (some) other objects?

In defining variable of a list object, for example:

x = [1,2,0.2,3,4]
y = x
x.sort()


I would expect that y is still equal to [1, 2, 0.2, 3, 4], but it does not. The value of y changed as x changed. To counter this, I found that using y = x.copy() can preserve the value in the first line.

On the other hand, another example :

x = 5
y = x
x = 4


from this the value of y is still 5, it does not change as x change.

My question : is this due to the design in list's class, or there is another explanation? I found the dynamic change also happen when using x.append(value). Any insight is appreciated. Regards, Arief

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