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The OrderedDict is a subclass of dict object in Python. The only difference between OrderedDict and dict is that, in OrderedDict, it maintains the orders of keys as inserted. In the dict, the ordering may or may not be happen. The OrderedDict is a standard library class, which is located in the collections module.
OrderedDict is part of python collections module. We can create an empty OrderedDict and add items to it. If we create an OrderedDict by passing a dict argument, then the ordering may be lost because dict doesn't maintain the insertion order. If an item is overwritten in the OrderedDict, it's position is maintained.
Intent signaling: If you use OrderedDict over dict , then your code makes it clear that the order of items in the dictionary is important. You're clearly communicating that your code needs or relies on the order of items in the underlying dictionary.
Standard dict objects preserve order in the reference (CPython) implementations of Python 3.5 and 3.6, and this order-preserving property is becoming a language feature in Python 3.7.
You are creating a dictionary first, then passing that dictionary to an OrderedDict. For Python versions < 3.6 (*), by the time you do that, the ordering is no longer going to be correct. dict is inherently not ordered.
Pass in a sequence of tuples instead:
ship = [("NAME", "Albatross"),
("HP", 50),
("BLASTERS", 13),
("THRUSTERS", 18),
("PRICE", 250)]
ship = collections.OrderedDict(ship)
What you see when you print the OrderedDict is it's representation, and it is entirely correct. OrderedDict([('PRICE', 250), ('HP', 50), ('NAME', 'Albatross'), ('BLASTERS', 13), ('THRUSTERS', 18)]) just shows you, in a reproducable representation, what the contents are of the OrderedDict.
(*): In the CPython 3.6 implementation, the dict type was updated to use a more memory efficient internal structure that has the happy side effect of preserving insertion order, and by extension the code shown in the question works without issues. As of Python 3.7, the Python language specification has been updated to require that all Python implementations must follow this behaviour. See this other answer of mine for details and also why you'd still may want to use an OrderedDict() for certain cases.
If you can't edit this part of code where your dict was defined you can still order it at any point in any way you want, like this:
from collections import OrderedDict
order_of_keys = ["key1", "key2", "key3", "key4", "key5"]
list_of_tuples = [(key, your_dict[key]) for key in order_of_keys]
your_dict = OrderedDict(list_of_tuples)
Most of the time we go for OrderedDict when we required a custom order not a generic one like ASC etc.
Here is the proposed solution:
import collections
ship = {"NAME": "Albatross",
"HP":50,
"BLASTERS":13,
"THRUSTERS":18,
"PRICE":250}
ship = collections.OrderedDict(ship)
print ship
new_dict = collections.OrderedDict()
new_dict["NAME"]=ship["NAME"]
new_dict["HP"]=ship["HP"]
new_dict["BLASTERS"]=ship["BLASTERS"]
new_dict["THRUSTERS"]=ship["THRUSTERS"]
new_dict["PRICE"]=ship["PRICE"]
print new_dict
This will be output:
OrderedDict([('PRICE', 250), ('HP', 50), ('NAME', 'Albatross'), ('BLASTERS', 13), ('THRUSTERS', 18)])
OrderedDict([('NAME', 'Albatross'), ('HP', 50), ('BLASTERS', 13), ('THRUSTERS', 18), ('PRICE', 250)])
Note: The new sorted dictionaries maintain their sort order when entries are deleted. But when new keys are added, the keys are appended to the end and the sort is not maintained.(official doc)
You can create the ordered dict from old dict in one line:
from collections import OrderedDict
ordered_dict = OrderedDict(sorted(ship.items())
The default sorting key is by dictionary key, so the new ordered_dict is sorted by old dict's keys.
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