code: def plus_replacement(random, population, parents, offspring, args):
      
      pool = list(offspring)
      pool.extend(parents)
      pool.sort(reverse=True)
      survivors = pool[:len(population)]
      return survivors
docs: Performs "plus" replacement.
      
      This function performs "plus" replacement, which means that
      the entire existing population is replaced by the best
      population-many elements from the combined set of parents and 
      offspring. 
      
      .. Arguments:
         random -- the random number generator object
         population -- the population of individuals
         parents -- the list of parent individuals
         offspring -- the list of offspring individuals
         args -- a dictionary of keyword arguments