CODEWITHSUNDEEP
python
Jesvin Jose
Jesvin Jose

Reputation: 23078

Order of list obtained by dictionary's keys()

Can I expect the keys() to remain in the same order?

I plan to use them for a dropdown box and I dont want them to shift if I add or delete items from the dictionary.

Upvotes: 4

Views: 143

Answers (6)

David Webb
David Webb

Reputation: 193696

The ordered of the keys in a dict is not guaranteed.

The documentation says:

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)...

The keys() method of a dictionary object returns a list of all the keys used in the dictionary, in arbitrary order (if you want it sorted, just apply the sorted() function to it).

Python 2.7+ and 3.1+ have the OrderedDict class in collections as described by PEP 372, which does exactly what you want. It remembers the order in which keys were added:

>>> from collections import OrderedDict
>>> od = OrderedDict()
>>> od[1] = "one"
>>> od[2] = "two"
>>> od[3] = "three"
>>> od.keys()
[1, 2, 3]

Upvotes: 3

Nadir Sampaoli
Nadir Sampaoli

Reputation: 5555

From python docs:

The keys() method of a dictionary object returns a list of all the keys used in the dictionary, in arbitrary order (if you want it sorted, just apply the sorted() function to it).

So a way to solve this issue would be to sort the keys as soon as you "listify" them.

Upvotes: 1

nickgroenke
nickgroenke

Reputation: 1502

You may want to try something like an array of dictionaries or objects. Arrays are ordered. The text for the menu item would be in some field of the array or object.

Upvotes: 0

dreadsci
dreadsci

Reputation: 54

No, not from one day to the next. keys() will be in an arbitrary order (although I think they might be consistent over the instance's lifetime, but that won't work for your menu).

Python3 has ordered dictionaries: collections.OrderedDict documentation

Upvotes: 1

David Wolever
David Wolever

Reputation: 154484

No. At least in cpython (and most likely every other implementation) you definitely can't. If you want guaranteed order, check out odict, which does guarantee order.

Upvotes: 1

BrenBarn
BrenBarn

Reputation: 251373

No. According to the documentation:

Keys and values are listed in an arbitrary order which is non-random, varies across Python implementations, and depends on the dictionary’s history of insertions and deletions.

Upvotes: 5

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