title: "TypeError: 'int' object is not iterable" even tough im not doing iteration
body: <p>so i'm just learning state machine from ocw.mit.edu course 6.01SC, so itry write this code</p>
  
  <pre><code>class sm(object):
  def start(self):
      self.state = self.startState
  def step(self, input):
      (s,o) = self.getNextValues(self.state, input)
      self.state = s
      return o
  def transduce(self, inputs):
      self.start()
      return [self.step(input) for input in inputs]
  
  class delay(sm):
      def __init__(self,v0):
          self.startState = v0
      def getNextValues(self, state, input):
          return (input, state)
  
  class cascade(sm):
      def __init__(self, a, b):
          self.startState = 0
          self.a = a
          self.b = b
          self.a.start()
          self.b.start()
      def getNextValues(self, state, input):
          return self.b.step(self.a.step(input))
  a = delay(1)
  b = delay(2)
  c = cascade(a,b)
  print(c.transduce([3,5,7,9]))
  </code></pre>
  
  <p>i try to cascade a and b, but i get "TypeError: 'int' object is not iterable" even tough i didn't create ant iteration. i've tried to debug and couldn't find it. please help. thanks!</p>