code: def Exp(self, m=None):
          
          if not self.log:
              raise ValueError("Pmf/Hist not under a log transform")
          self.log = False
  
          if m is None:
              m = self.MaxLike()
  
          for x, p in self.d.iteritems():
              self.Set(x, math.exp(p - m))
docs: Exponentiates the probabilities.
  
          m: how much to shift the ps before exponentiating
  
          If m is None, normalizes so that the largest prob is 1.