https://gist.github.com/limitedmage/945473
Python Quantum Computing simulator, Juliana Pena, 2011.
Two qubits and superdense coding protocol example.

Errata:

 TwoQubit measure():
 
  zerozeroprob = abs(self.zerozero) ** 2
  zerooneprob  = abs(self.zeroone)  ** 2
  onezeroprob  = abs(self.onezero)  ** 2
 
 should be:
 
  zerozeroprob = abs(self.zerozero) ** 2
  zerooneprob  = abs(self.zeroone)  ** 2 + zerozeroprob # cumulative distribution
  onezeroprob  = abs(self.onezero)  ** 2 + zerooneprob