code: def get_checkcode(cls, card_number_str):
          
          total = 0
          even = True
  
          for item in card_number_str[-1::-1]:
              item = int(item)
              if even:
                  item <<= 1
              if item > 9:
                  item -= 9
              total += item
              even = not even
  
          checkcode = (10 - (total % 10)) % 10
  
          return str(checkcode)
docs: 计算银行卡校验位；
  
          :param:
              * card_number_str: (string) 要查询的银行卡号
          :returns:
              checkcode: (string) 银行卡的校验位
  
          举例如下::
  
              from fishbase.fish_data import *
  
              print('--- fish_data get_checkcode demo ---')
  
              # 不能放真的卡信息，有风险
              print(CardBin.get_checkcode('439188000699010'))
  
              print('---')
  
          输出结果::
  
              --- fish_data get_checkcode demo ---
              9
              ---