list slice is copy

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examples/lists/list_slice_is_copy.py

x = [1, 1, 2, 3, 5, 8, 13, 21, 34]
y = x[2:5]
print(y)    # [2, 3, 5]

x[2] = 20
print(x)    # [1, 1, 20, 3, 5, 8, 13, 21, 34]
print(y)    #  [2, 3, 5]