Python3.x 为什么字典排序是不确定的

Update:在Python 3.6中，dict有一个保留插入顺序的new implementation.在Python 3.7中，这种保序行为是guaranteed:

dict个对象has been declared的插入顺序保留性质将成为Python语言规范的正式部分.

这是2012年的security fix分的结果，在Python 3.3中是enabled by default分(向下滚动到"安全改进").

从公告中:

散列随机化导致dict和set的迭代顺序为

如上所述，最后一个大写的位在Python 3.3中不再正确.

See also: object.__hash__() documentation("注意"侧栏).

如果绝对必要，可以通过将PYTHONHASHSEED环境变量设置为0，在受此行为影响的Python版本中禁用哈希随机化.

你的反例是:

list({str(i): i for i in range(10)}.keys())

…在Python 3.3中，not实际上总是给出相同的结果，尽管不同排序的数量受到哈希冲突处理方式的限制:

$ for x in {0..999}
> do
>   python3.3 -c "print(list({str(i): i for i in range(10)}.keys()))"
> done | sort | uniq -c
     61 ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
     73 ['1', '0', '3', '2', '5', '4', '7', '6', '9', '8']
     62 ['2', '3', '0', '1', '6', '7', '4', '5', '8', '9']
     59 ['3', '2', '1', '0', '7', '6', '5', '4', '9', '8']
     58 ['4', '5', '6', '7', '0', '1', '2', '3', '8', '9']
     55 ['5', '4', '7', '6', '1', '0', '3', '2', '9', '8']
     62 ['6', '7', '4', '5', '2', '3', '0', '1', '8', '9']
     63 ['7', '6', '5', '4', '3', '2', '1', '0', '9', '8']
     60 ['8', '9', '0', '1', '2', '3', '4', '5', '6', '7']
     66 ['8', '9', '2', '3', '0', '1', '6', '7', '4', '5']
     65 ['8', '9', '4', '5', '6', '7', '0', '1', '2', '3']
     53 ['8', '9', '6', '7', '4', '5', '2', '3', '0', '1']
     62 ['9', '8', '1', '0', '3', '2', '5', '4', '7', '6']
     52 ['9', '8', '3', '2', '1', '0', '7', '6', '5', '4']
     73 ['9', '8', '5', '4', '7', '6', '1', '0', '3', '2']
     76 ['9', '8', '7', '6', '5', '4', '3', '2', '1', '0']

正如本答案开头所指出的，Python 3.6中不再是这种情况:

$ for x in {0..999}
> do
>   python3.6 -c "print(list({str(i): i for i in range(10)}.keys()))"
> done | sort | uniq -c
   1000 ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']