How to use python actor in BCVTB

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Hi, I was trying to learn how to use python actor in BCVTB. So I tried to take two constants ( x and y ), pass them as variables to python actor, add them using python script and plot a graph which should be a constant line. The python script that I have below gives me a TypeError. I can't seem to understand why '+' is not being recognised as an operand. I am also attaching the screenshots of individual actors and the system xml file. Can you please tell me where my problem lies ? My python script looks like:

class Main :
  def fire(self) :

    if not self.input.hasToken(0) :
      return
    t = self.input.get(0)
    x = self.cons2.get(0)
    y = int(t) + int(x)
    self.output.broadcast(t)

But this gives me a TypeError.