code: def calculate_vss(self, method=None):
          
          if self.variance == float(0):
              return self.vss
          else:
              # Calculate gausian distribution and return
              if method == "gaussian" or method is None:
                  return gauss(self.vss, self.variance)
              elif method == "random":
                  return uniform(self.vss - self.variance, self.vss + self.variance)
              else:
                  raise ValueError("Method of vss calculation not recognized, please use 'gaussian' or 'random'")
docs: Calculate the vertical swimming speed of this behavior.
          Takes into account the vertical swimming speed and the
          variance.
  
          Parameters:
              method:  "gaussian" (default) or "random"
                       "random" (vss - variance) < X < (vss + variance)