Question

我有一个类，其中两个变量设置为某个默认值。我已经定义了一个函数，我在函数中将这些变量声明为全局变量。我得到这个错误，说明变量没有定义。一个变量是counter，它将在每个函数调用时递增，而其他变量必须在每次调用时附加消息。在追加多条消息并且计数器值达到某个阈值后，我想将所有这些消息插入到MySQL数据库中。但是变量没有附加值。它显示变量未定义。

class Message():
     insertStatement= ''
     insertCounter = 0

    def Save(self, msg)
        global insertCounter
        global insertStatement 

        if  msg.topic.startswith("topic1/"):
            insertStatement += "INSERT INTO mydatabase.table VALUES (" + msg.payload.decode("utf-8") + "," + datetime + ");"
       elif msg.topic.startswith("topic2/"):
            insertStatement += "INSERT INTO mydatabase.table1 VALUES (" + msg.payload.decode("utf-8") + "," + datetime + ");"
       elif msg.topic.startswith("topic3/")   
            insertStatement += "INSERT INTO mydatabase.table2 VALUES (" +msg.payload.decode("utf-8") + "," + datetime + ");"
       elif msg.topic.startswith("messages"):
            insertStatement += "INSERT INTO mydatabase.table3 VALUES ('" + msg.topic + "',"  + msg.payload.decode("utf-8") + "," + datetime + ");"
       else:
            return  
       insertcounter +=1
       if(insertCounter > 1000):
         for result in cursor.execute(insertStatement, multi=True):
             print result.row_count  # i changed it to result

Answer 1

请检查最后一行。它应该是result而不是reslut。

Answer 2

您可能只需要实例变量：

class Message():
    def __init__(self):
        self.insertStatement= ''
        self.insertCounter = 0

    def Save(self, msg)
        if msg.topic.startswith("topic1/"):
            self.insertStatement += "INSERT INTO mydatabase.table VALUES (" + msg.payload.decode("utf-8") + "," + datetime + ");"
        elif msg.topic.startswith("topic2/"):
            self.insertStatement += "INSERT INTO mydatabase.table1 VALUES (" + msg.payload.decode("utf-8") + "," + datetime + ");"
        elif msg.topic.startswith("topic3/")   
            self.insertStatement += "INSERT INTO mydatabase.table2 VALUES (" +msg.payload.decode("utf-8") + "," + datetime + ");"
        elif msg.topic.startswith("messages"):
            self.insertStatement += "INSERT INTO mydatabase.table3 VALUES ('" + msg.topic + "',"  + msg.payload.decode("utf-8") + "," + datetime + ");"
        else:
            return  
        self.insertcounter += 1
        if self.insertCounter > 1000:
            # do the SQL thing

作为一名程序员，你应该尝试非常非常非常很难不使用全局变量。

Answer 3

您的代码中有几个拼写错误，请更新并检查。

您已声明全局变量72px × 72px并递增变量insertCounter。将其更新为insertcounter
更新结果变量，假设为self.insertCounter+1，而不是result

Answer 4

变量insertStatement和insertCounter是类变量。您不必将它们作为全局内部Save()引用。要访问这些类变量，请使用Message.insertStatement和Message.insertCounter

 class Message():
         insertStatement= ''
         insertCounter = 0

        def Save(self, msg):

            if  msg.topic.startswith("topic1/"):
                Message.insertStatement += "INSERT INTO mydatabase.table VALUES (" + msg.payload.decode("utf-8") + "," + datetime + ");"
           elif msg.topic.startswith("topic2/"):
                Message.insertStatement += "INSERT INTO mydatabase.table1 VALUES (" + msg.payload.decode("utf-8") + "," + datetime + ");"
           elif msg.topic.startswith("topic3/")   
                Message.insertStatement += "INSERT INTO mydatabase.table2 VALUES (" +msg.payload.decode("utf-8") + "," + datetime + ");"
           elif msg.topic.startswith("messages"):
                Message.insertStatement += "INSERT INTO mydatabase.table3 VALUES ('" + msg.topic + "',"  + msg.payload.decode("utf-8") + "," + datetime + ");"
           else:
                return  
           Message.insertcounter +=1
           if(Message.insertCounter > 1000):
             for result in cursor.execute(Message.insertStatement, multi=True):
                 print result.row_count  # i changed it to result

Python错误：类undefined中的全局变量

4 个答案: