TypeError in Chain.communication_classes()

[rdbliss]

When running Chain.communication_classes(), a TypeError is thrown: TypeError: unhashable type: 'set'.

The issue seems to be having nested sets, since the interior sets are mutable. One fix would be to use frozenset() for the nested sets. Alternatively, the return could be changed to a list of sets, nested lists, or something similar.

Exact error:

In [1]: run pykov.py

In [2]: Chain({(0, 1): 1, (1, 0): 1}).communication_classes()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-cc5c171ee32c> in <module>()
----> 1 Chain({(0, 1): 1, (1, 0): 1}).communication_classes()

/home/rwb/python/Pykov/pykov.py in communication_classes(self)
   1347                 if row[0, el] == 1:
   1348                     comm_class.add(pos2el[el])
-> 1349             res.add(comm_class)
   1350         return res
   1351 

TypeError: unhashable type: 'set'

[riccardoscalco]

Thanks for pointing out that.
@awilsoncs, do you have any preference on the possible fix?