title: Type error Unhashable type:set
body: <p>The below code has an error in function U=set(p.enum()) which a type error of unhashable type : 'set' actually if you can see the class method enum am returning 'L' which is list of sets and the U in function should be a set so can you please help me to resolve the issue or How can I convert list of sets to set of sets?     </p>
  
  <pre><code>class pattern(object):
  
          def __init__(self,node,sets,cnt):
              self.node=node
              self.sets=sets
              self.cnt=cnt
  
          def enum(self):
              L=[]
              if self.cnt==1:
                  L = self.node
              else:
                  for i in self.sets:
                      L=[]
                      for j in self.node:
                          if i!=j:
                              L.append(set([i])|set([j]))
  
              return L #List of sets              
  
      V=set([1,2,3,4])
      U=set()
      cnt=1
      for j in V:
          p=pattern(V,(U|set([j])),cnt)
          U=set(p.enum()) #type error Unhashable type:'set'   
          print U
              cnt+=1 
  </code></pre>