list()将传递给它的iterable转换为列表。如果itertable已经是一个列表，则返回 ，即仅最外层的容器是新的，其余对象仍然相同。
>>> t = (1,2,3,4,[5,6,7,8],9)
>>> lst = list(t)
>>> lst[4] is t[4] #outermost container is Now a list() but inner items are still same.
True
>>> lst1 = [[[2,3,4]]]
>>> id(lst1)
140270501696936
>>> lst2 = list(lst1)
>>> id(lst2)
140270478302096
>>> lst1[0] is lst2[0]
True
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