列表的复制

>>> list_a=[1,2,3,4]
>>> list_a
[1, 2, 3, 4]
>>> list_b=list_a
>>> list_b
[1, 2, 3, 4]
>>> list_a.append(1)
>>> list_a
[1, 2, 3, 4, 1]
>>> list_b
[1, 2, 3, 4, 1]