Python: order in a set of numbers

Question

With this code:

print set(a**b for a in range(2, 5) for b in range(2, 5))

I get this answer:

set([64, 256, 4, 8, 9, 16, 81,         


        

Answer 1

Sets are by their nature unordered containers. From the documentation:

A set object is an unordered collection of distinct hashable objects.

They are implemented using a hash table, facilitating O(1) membership tests. If you need an ordered set, try OrderedDict.fromkeys():

from collections import OrderedDict
OrderedDict.fromkeys(a**b for a in range(2, 5) for b in range(2, 5))