Slice assignment modifes original list

Question

There is this code:

a = [1, 2, 3, 4, 5]
a[:] = [] # and now a is also empty

Statement a[:] creates a copy of list a as I read, so if empty list [] is assigned to the copy then why original object is also modified?

Answer 1

x = a[:] makes x a new list containing the same values as a

a[:] = x makes the existing list a contain the same values as x

The behaviour of an expression changes when it switches sides of the equals.