title: What does "Killed: 9" error mean?
body: <p>I am writing a program to find all the subsets of a given string. However it is resulting in an error called <code>Killed: 9</code>.</p>
  
  <pre><code>class Strings(object):
      def __init__(self,string):
          self.list1=[]
          self.string=string
  
      def appendToList(self,ch1):
          self.list1.append(ch1)
          for i in self.list1:
              self.list1.append(i+ch1)
  
      def subset(self):
          for ch in self.string:
              self.list1=self.appendToList(ch)
          print self.list1
  
  obj=Strings('hello')
  obj.subset()
  </code></pre>