In Python, how to I iterate over a dictionary in sorted order?

Question

There's an existing function that ends in:

return dict.iteritems()

that returns an unsorted iterator for a given dictionary. I would like to return an iterator that goes through the items in sorted order. How do I do that?

Answer 1

Use the sorted() function:

return sorted(dict.iteritems())

If you want an actual iterator over the sorted results, since sorted() returns a list, use:

return iter(sorted(dict.iteritems()))

Answer 2

Greg's answer is right. Note that in Python 3.0 you'll have to do

sorted(dict.items())

as iteritems will be gone.

Answer 3

A dict's keys are stored in a hashtable so that is their 'natural order', i.e. psuedo-random. Any other ordering is a concept of the consumer of the dict.

sorted() always returns a list, not a dict. If you pass it a dict.items() (which produces a list of tuples), it will return a list of tuples [(k1,v1), (k2,v2), ...] which can be used in a loop in a way very much like a dict, but it is not in anyway a dict!

foo = {
    'a':    1,
    'b':    2,
    'c':    3,
    }

print foo
>>> {'a': 1, 'c': 3, 'b': 2}

print foo.items()
>>> [('a', 1), ('c', 3), ('b', 2)]

print sorted(foo.items())
>>> [('a', 1), ('b', 2), ('c', 3)]

The following feels like a dict in a loop, but it's not, it's a list of tuples being unpacked into k,v:

for k,v in sorted(foo.items()):
    print k, v

Roughly equivalent to:

for k in sorted(foo.keys()):
    print k, foo[k]

Answer 4

Haven't tested this very extensively, but works in Python 2.5.2.

>>> d = {"x":2, "h":15, "a":2222}
>>> it = iter(sorted(d.iteritems()))
>>> it.next()
('a', 2222)
>>> it.next()
('h', 15)
>>> it.next()
('x', 2)
>>>

Answer 5

sorted returns a list, hence your error when you try to iterate over it, but because you can't order a dict you will have to deal with a list.

I have no idea what the larger context of your code is, but you could try adding an iterator to the resulting list. like this maybe?:

return iter(sorted(dict.iteritems()))

of course you will be getting back tuples now because sorted turned your dict into a list of tuples

ex: say your dict was: {'a':1,'c':3,'b':2} sorted turns it into a list:

[('a',1),('b',2),('c',3)]

so when you actually iterate over the list you get back (in this example) a tuple composed of a string and an integer, but at least you will be able to iterate over it.