Python:AttributeError:“str”对象在for循环内部调用方法时没有属性

Question

当我尝试使用for循环生成的名称访问类实例时，我得到

"AttributeError: 'str' object has no attribute".

我是Python新手，请原谅任何“不是最佳实践”。谢谢你的帮助

class Csv:
    def __init__(self, invoicenum, customer, invoicedate, duedate, description, amount, productservice, invoiceclass):
        self.invoicenum = invoicenum
        self.customer = customer
        self.invoicedate = invoicedate
        self.duedate = duedate
        self.description = description
        self.amount = amount
        self.productservice = productservice
        self.invoiceclass = invoiceclass
        self.line = '{},{},{},{},{},{},{},{}\n'.format(invoicenum, customer, invoicedate,
                                                       duedate, description, amount, productservice, invoiceclass)

    def wite_to_db(self):
        mydb = mysql.connector.connect(host="localhost", user="root",
                                       passwd="passwd", database="invoice")
        mycursor = mydb.cursor()
        sql = "insert into invoice " "(Invoice_no, Customer, Invoice_Date, Due_date, Description, Amount, Product_service, Class)" "VALUES (%s,%s,%s,%s,%s,%s,%s,%s)"
        val = (self.invoicenum, self.customer, self.invoicedate, self.duedate,
               self.description, self.amount, self.productservice, self.invoiceclass)
        mycursor.execute(sql, val)
        mydb.commit()


x0 = Csv("1355", "Test1 User", "2020-05-03", "2020-12-31", 7095, 300, "Tithe", "General Fund")
x1 = Csv("1124", "Test2 User", "2020-05-03", "2020-12-31", 7095, 300, "Tithe", "General Fund")
x2 = Csv("14432", "Test3 User", "2020-05-03", "2020-12-31", 7095, 300, "Tithe", "General Fund")
x3 = Csv("1312", "Test4 User", "2020-05-03", "2020-12-31", 7095, 300, "Tithe", "General Fund")


line_range = range(4)

for line in line_range:
    line_instance = 'x' + str(line)
    print(line_instance)
    line_instance.write_to_db()

Answer 1

line_instance = 'x' + str(line)
print(line_instance)
line_instance.write_to_db()

这是错误的。字符串没有write_to_db方法。您在Csv类中定义了这个方法（或者更确切地说是一个名称非常相似的wite_to_db…），但是line_instance显然是一个字符串，而不是Csv类的实例。您可能想要做的是：

for line_instance in (x0, x1, x2, x3):
    line_instance.write_to_db()

Answer 2

line\u实例是一个str。 str没有名为write\u to\u db的函数

Answer 3

您所做的是，当您创建line_instance变量时，将其设置为字符串，然后几行之后，您实际上尝试在Csv类中对字符串运行函数-write_to_db。这就是错误发生的原因

我可以推荐做以下几点：

x0 = Csv(...
x1 = Csv(...
x2 = Csv(...
x3 = Csv(...

x_list = [x0, x1, x2, x3]

for x in x_list:
    x.write_to_db()

旁注，您在Csv类中的“wite_to_db”函数中的定义有一个输入错误