Does Python have an ordered set?

Question

Python has an ordered dictionary. What about an ordered set?

Answer 1

Yes, python has an ordered set and they run on Py2.6 or later and 3.0 or later without any modifications. The interface is almost exactly the same as a normal set, except that initialisation should be done with a list.

OrderedSet([1, 2, 3])

This is a MutableSet, so the signature for .union doesn't match that of set, but since it includes __or__ something similar can easily be added:

@staticmethod 

def union(*sets): 

   union = OrderedSet() 

   union.union(*sets) 

   return union 

def union(self, *sets):

   for set in sets: 

       self |= set