Is numeric keys of Python's dictionary automatically sorted?

[John]

I am coding a radix sort in python and I think that Python's dictionary may 
be a choice for bucket.

The only problem is that dictionary is a mapping without order. But I just 
found that if the keys are numeric, the keys themselves are ordered in the 
dictionary.

part of my code is like this:
radix={}
    for i in range(256):
        radix[i]=[]

I checked and found that it is ordered like: {1:[], 2:[], 3[],...}

So I can just print out the contents of the dictionary in the desired order 
without additional code.
I also tried adding new numeric keys and found that the dictionary's keys 
are still ordered.

However, I am not sure whether it is always like this. Can anybody confirm 
my finding?