python技巧 is 和 ==
- is 判断变量是否指向同一个对象
- == 判断变量引用的对象是否相等
In [2]: a=[1,2] In [3]: b=a In [4]: a == b Out[4]: True In [5]: a is b Out[5]: True In [6]: c = list(a) In [7]: a == c Out[7]: True In [8]: a is c Out[8]: False In [9]: b is c Out[9]: False

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In [2]: a=[1,2] In [3]: b=a In [4]: a == b Out[4]: True In [5]: a is b Out[5]: True In [6]: c = list(a) In [7]: a == c Out[7]: True In [8]: a is c Out[8]: False In [9]: b is c Out[9]: False