code: def crossover_template(cls, length, points=2):
          
  
          assert isinstance(length, int) and length >= 0
          assert isinstance(points, int) and points >= 0
  
          # Select the crossover points.
          points = random.sample(range(length + 1), points)
  
          # Prep the points for the loop.
          points.sort()
          points.append(length)
  
          # Fill the bits in with alternating ranges of 0 and 1 according to
          # the selected crossover points.
          previous = 0
          include_range = bool(random.randrange(2))
          pieces = []
          for point in points:
              if point > previous:
                  fill = (numpy.ones if include_range else numpy.zeros)
                  pieces.append(fill(point - previous, dtype=bool))
              include_range = not include_range
              previous = point
          bits = numpy.concatenate(pieces)
          bits.flags.writeable = False
  
          return cls(bits)
docs: Create a crossover template with the given number of points. The
          crossover template can be used as a mask to crossover two
          bitstrings of the same length.
  
          Usage:
              assert len(parent1) == len(parent2)
              template = BitString.crossover_template(len(parent1))
              inv_template = ~template
              child1 = (parent1 & template) | (parent2 & inv_template)
              child2 = (parent1 & inv_template) | (parent2 & template)
  
          Arguments:
              length: An int, indicating the desired length of the result.
              points: An int, the number of crossover points.
          Return:
              A BitString instance of the requested length which can be used
              as a crossover template.