code: def grid_str(self, path=None, start=None, end=None,
                   border=True, start_chr='s', end_chr='e',
                   path_chr='x', empty_chr=' ', block_chr='#',
                   show_weight=False):
          
          data = ''
          if border:
              data = '+{}+'.format('-'*len(self.nodes[0]))
          for y in range(len(self.nodes)):
              line = ''
              for x in range(len(self.nodes[y])):
                  node = self.nodes[y][x]
                  if node == start:
                      line += start_chr
                  elif node == end:
                      line += end_chr
                  elif path and ((node.x, node.y) in path or node in path):
                      line += path_chr
                  elif node.walkable:
                      # empty field
                      weight = str(node.weight) if node.weight < 10 else '+'
                      line += weight if show_weight else empty_chr
                  else:
                      line += block_chr  # blocked field
              if border:
                  line = '|'+line+'|'
              if data:
                  data += '\n'
              data += line
          if border:
              data += '\n+{}+'.format('-'*len(self.nodes[0]))
          return data
docs: create a printable string from the grid using ASCII characters
  
          :param path: list of nodes that show the path
          :param start: start node
          :param end: end node
          :param border: create a border around the grid
          :param start_chr: character for the start (default "s")
          :param end_chr: character for the destination (default "e")
          :param path_chr: character to show the path (default "x")
          :param empty_chr: character for empty fields (default " ")
          :param block_chr: character for blocking elements (default "#")
          :param show_weight: instead of empty_chr show the cost of each empty
                              field (shows a + if the value of weight is > 10)
          :return: