python - Looping seems to not follow sequence

Question

I feel like I'm missing something obvious here!

seq = {'a': ['1'], 'aa': ['2'], 'aaa': ['3'], 'aaaa': ['4'], 'aaaaa': ['5']}
for s in seq:
    print(s)

outputs:

a
aa
aaaa
aaaaa
aaa

Whereas surely it should output:

a
aa
aaa
aaaa
aaaaa

What's going wrong here?

Answer 1

Dictionaries are not ordered. If you need to rely on the ordering, you need an OrderedDict - there's one in the collections module in Python 2.7, or you can use one of the many recipes around.