code: def step(self):
          
  
          # Probability and likelihood for s's current value:
  
          if self.verbose > 2:
              print_()
              print_(self._id + ' getting initial logp.')
  
          if self.proposal_distribution == "prior":
              logp = self.loglike
          else:
              logp = self.logp_plus_loglike
  
          if self.verbose > 2:
              print_(self._id + ' proposing.')
  
          # Sample a candidate value
          self.propose()
  
          # Probability and likelihood for s's proposed value:
          try:
              if self.proposal_distribution == "prior":
                  logp_p = self.loglike
                  # Check for weirdness before accepting jump
                  if self.check_before_accepting:
                      self.stochastic.logp
              else:
                  logp_p = self.logp_plus_loglike
  
          except ZeroProbability:
  
              # Reject proposal
              if self.verbose > 2:
                  print_(self._id + ' rejecting due to ZeroProbability.')
              self.reject()
  
              # Increment rejected count
              self.rejected += 1
  
              if self.verbose > 2:
                  print_(self._id + ' returning.')
              return
  
          if self.verbose > 2:
              print_('logp_p - logp: ', logp_p - logp)
  
          HF = self.hastings_factor()
  
          # Evaluate acceptance ratio
          if log(random()) > logp_p - logp + HF:
  
              # Revert s if fail
              self.reject()
  
              # Increment rejected count
              self.rejected += 1
              if self.verbose > 2:
                  print_(self._id + ' rejecting')
          else:
              # Increment accepted count
              self.accepted += 1
              if self.verbose > 2:
                  print_(self._id + ' accepting')
  
          if self.verbose > 2:
              print_(self._id + ' returning.')
docs: The default step method applies if the variable is floating-point
          valued, and is not being proposed from its prior.