code: def expand(self,x,y,z):
          
          if x != None:
              if self.minx is None or x < self.minx:
                  self.minx = x
              if self.maxx is None or x > self.maxx:
                  self.maxx = x
          if y != None:
              if self.miny is None or y < self.miny:
                  self.miny = y
              if self.maxy is None or y > self.maxy:
                  self.maxy = y
          if z != None:
              if self.minz is None or z < self.minz:
                  self.minz = z
              if self.maxz is None or z > self.maxz:
                  self.maxz = z
docs: Expands the bounding