I have a dictionary
{'a': 'first', 'b': 'second'}
However, I need the dictionary in a different order:
{'b': 'second', 'a': 'first'}
What is the best way to do this?
28
votes
Ok, my fault, I'll read documentation. I just print it and it was out by specific order by chance. I thought it has something to do with a way it is written. Like php's array.
- Qiao
@Qiao This is actually a good question. I was like "oh, that'll be easy to answer with the documentation" -- it isn't. This "trivial fact" seems to be assumed knowledge in most places. The best I can find (in OrderedDict, chapter 8.3) is "An OrderedDict is a dict that remembers the order that keys were first inserted.".
- user166390
Ahh, there it is: "It is best to think of a dictionary as an unordered set of key: value pairs, with the requirement that the keys are unique (within one dictionary)." from 5.5 Data Structures in the Tutorial.
- user166390
-1. Searching StackOverflow for "python dictionary order" easily finds the answer. You should at least try something before posting to StackOverflow.
- Steven Rumbalski
possible duplicate of In what order does python display dictionary keys?
- dawg
3 Answers
41
votes
Dictionaries are not ordered. So there is no way to do it.
If you have python2.7+, you can use collections.OrderedDict - in this case you could retrieve the item list using .items() and then reverse it and create a new OrderedDict from the reversed list:
>>> od = OrderedDict((('a', 'first'), ('b', 'second')))
>>> od
OrderedDict([('a', 'first'), ('b', 'second')])
>>> items = od.items() # list(od.items()) in Python3
>>> items.reverse()
>>> OrderedDict(items)
OrderedDict([('b', 'second'), ('a', 'first')])
If you are using an older python version you can get a backport from http://code.activestate.com/recipes/576693/
7
votes
