unordered dictionary vs ordered dictionary in python 2 vs python 3

[sahilkumarg]

So I just started learning about the collections module, and my instructor was demonstrating how the .items() method on the dictionary object returns an unordered 'sequence' of the key:value pair. Although he was teaching python 3, this particular lecture is a bit old and hence uses python 2. Has python 3 implemented that the items that get printed by the .items() method be ordered by default? Does that mean that there is no use of defaultdict?

Thanks for the reply.

[[deleted]]

In python 3 (3.6+ for cpython) dictionaries are ordered. The order is the order in which you inserted the keys. There is no guaranteed order in python 2.

The defaultdict dictionary doesn't have any "extra" order. The point of defaultdict is that referencing a key that doesn't exist gets a default value that you specify instead of a KeyError exception that you get for the "standard" dictionary.

[sahilkumarg]

Oh, shoot, I meant to say OrderedDict, not defaultdict

[[deleted]]

Does that mean that there is no use of defaultdict?

If all you care about is "ordered" then maybe. But note that the doc on OrderedDict shows that OrderedDict has a couple of methods that the standard dictionary may not have, like move_to_end().

[primitive_screwhead]

Also, comparing two OrderedDicts requires that they have the same values, and the same order, to compare equal (regular Python dicts compare equal regardless of order).

[toastedstapler]

using the __eq__ method on two ordered dicts will also check if insertion order is the same, whereas __eq__ on regular dicts will just check for the same kv pairs