为什么cursor.execute只执行一次并在这种情况下返回？

Question

def SimplifyTrainUser(self): 
    self.cursor.execute('SELECT user_id, item_id, look, store, cart, buy FROM user_features limit 0, 50') 
    while True: 
     str=self.cursor.fetchone() 
     if str: 
      look_times = len(str['look'].split(',')) if str['look'] else 0 
      store_times = len(str['store'].split(',')) if str['store'] else 0 
      cart_times = len(str['cart'].split(',')) if str['cart'] else 0 
      buy_times = len(str['buy'].split(',')) if str['buy'] else 0 
      lru = max(str['look'].split(',') + str['store'].split(',') + str['cart'].split(',') + str['buy'].split(',')) 
      user_id = str['user_id'] 
      item_id = str['item_id'] 

      if not (look_times <=4 and store_times <=1 and cart_times == 0 and buy_times == 0 and int(lru) <= 15): 
        self.cursor.execute('INSERT INTO pure_data VALUES(%s,%s,%s,%s,%s,%s)', (user_id, item_id, str['look'], 
              str['store'], str['cart'], str['buy'])) 
        self.db.commit() 
        print "once" 
        global DELETE_INDEX 
     else: 
      return 0 

self.cursor.execute('INSERT INTO pure_data VALUES(%s,%s,%s,%s,%s,%s)', (user_id, item_id, str['look'],str['store'], str['cart'], str['buy']))只执行一次。如果我评论它，“一次”可以打印29次。是什么原因？

Answer 1

我找到了原因。每当调用cursor.execute时，都会移动光标。

当INSERT INTO pure_data时，str=self.cursor.fetchone()等于0，循环结束。