python - OrderedDict 键错误

Question

import collections

d = collections.defaultdict(dict)

d["i"]["a"] = "111"
d["i"]["b"] = "222"

print d

od = collections.OrderedDict()

od["i"]["a"] = "111"
od["i"]["b"] = "222"

print od

输出:

defaultdict(<type 'dict'>, {'i': {'a': '111', 'b': '222'}})
Traceback (most recent call last):
  File "app_main.py", line 51, in run_toplevel
  File "/Users/adam/Desktop/collections.py", line 12, in <module>
    od["i"]["a"] = "111"
KeyError: 'i'

为什么 OrderedDict 会出现关键错误以及我可以采取什么措施？

谢谢。

Answer 1

OrderedDict 并不是 defaultdict。你必须做这样的事情:

import collections
od = collections.OrderedDict()
od["i"] = collections.OrderedDict()
od["i"]["a"] = "111"
od["i"]["b"] = "222"
print od

输出:

OrderedDict([('i', OrderedDict([('a', '111'), ('b', '222')]))])

参见this answer潜在的有序 ​​defaultdict 实现。