code: def insert_characters(self, count=None):
          
          self.dirty.add(self.cursor.y)
  
          count = count or 1
          line = self.buffer[self.cursor.y]
          for x in range(self.columns, self.cursor.x - 1, -1):
              if x + count <= self.columns:
                  line[x + count] = line[x]
              line.pop(x, None)
docs: Insert the indicated # of blank characters at the cursor
          position. The cursor does not move and remains at the beginning
          of the inserted blank characters. Data on the line is shifted
          forward.
  
          :param int count: number of characters to insert.