python - OrderedDict 未订购？

Question

我正在尝试使用 OrderedDict，但它一直被乱序创建。例如，

from collections import OrderedDict
OrderedDict(a=1,b=2,c=3)

产量

OrderedDict([('a', 1), ('c', 3), ('b', 2)])

而不是预期

OrderedDict([('a', 1), ('b', 2), ('c', 3)])

如何确保它按照我想要的正确顺序创建？

Answer 1

collections.OrderedDict 跟踪添加元素的顺序。这将在循环中正常工作:

c = collections.OrderedDict()
for a,b in zip('abc', (1,2,3)):
    c[a] = b

但是，表达式 OrderedDict(a=1,b=2,c=3) 通过将几个关键字参数传递给它的构造函数来创建一个 OrderedDict。在 Python 2.7 中，不保证关键字参数的顺序。如果你想这样做，你将不得不迁移到 Python 3.6，它实现了 PEP 468，Preserving the order of **kwargs in a function .

The **kwargs syntax in a function definition indicates that the interpreter should collect all keyword arguments that do not correspond to other named parameters. However, Python does not preserved the order in which those collected keyword arguments were passed to the function. In some contexts the order matters. This PEP dictates that the collected keyword arguments be exposed in the function body as an ordered mapping.