代码1:
>>> l1=range(3)
>>> l2=l1
>>> l2+=[4]
>>> l1
[0, 1, 2, 4]
>>> l2
[0, 1, 2, 4]
代码2:
>>> l2=l1
>>> l2=l2+[4]
>>> l1
[0, 1, 2]
>>> l2
[0, 1, 2, 4]
Why does += behave unexpectedly on lists?
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