Python Mysql TypeError：“ NoneType”对象不可下标

Question

conn = MySQLdb.connect (host = "localhost", user="root", passwd="xxxx", db="xxxxx")
     cursor = conn.cursor()
     cursor.execute ("SELECT * FROM pin WHERE active=1")
     while (1):
       row = cursor.fetchone()
       st = str(row[2])
       pin = str(row[1])
       order = str(st)+str(pin)
       if row == None:
          break
       sendSerial(order)
conn.close()

为什么st = str（row [2]）变成错误？应该如何从数据库中将行检索到变量中？

谢谢您的回答。

Answer 1

st = str(row[2])错误是因为没有更多行时cursor.fetchone()返回None。

使用以下方法之一修复它：

row = cursor.fetchone()
while row:
    do_stuff()
    row = cursor.fetchone()

要么

for row in cursor:
    do_stuff()

要么

while True:
    row = cursor.fetchone()
    if row is None:  # better: if not row
          break
    do_stuff()