Question

我正在尝试在函数中创建项目对象，但是当我尝试打印出项目属性时，会出现错误。

    Traceback (most recent call last):
  File ".\AddSales.py", line 184, in <module>
    if (collectSerials(salesOrderInfo[0], salesOrderInfo[1], salesOrderInfo[2], itemInfo[0], itemInfo[1] ,itemList) == 1):
  File ".\AddSales.py", line 62, in collectSerials
    print(item.getName())
  File ".\AddSales.py", line 109, in getName
    return self.__name
AttributeError: 'Item' object has no attribute '_Item__name'

对象：课程项目：

def __init__(self, name, serialNumber, salesOrderNumber, shippingDate, salesInfo, warrantyExpiration):
    self.name = name
    self.serialNumber = serialNumber
    self.salesOrderNumber = salesOrderNumber
    self.shippingDate = shippingDate
    self.salesInfo = salesInfo
    self.warrantyExpiration = warrantyExpiration

功能：

def collectSerials(salesOrderNum, shipDate, info, name, warranty, workingList=None):
    while 1:
    sn = input("Scan in the item's serial number, or enter \"done\" if finished scanning: \n")
    if (sn == "done"):
        break
    item = Item(name, sn, salesOrderNum, shipDate, info, warranty)
    print(item.getName())
    if (workingList is None):
        workingList = []
    workingList.append(item)


answer = input("Choose between the following options (Enter the corresponding number): \n1) Enter a different product \n2)Exit and finish sales order\n")

return answer

函数调用：

collectSerials(salesOrderInfo[0], salesOrderInfo[1], salesOrderInfo[2], itemInfo[0], itemInfo[1] ,itemList)

Answer 1

在Python中为属性名称加上两个下划线（仅）时，会触发一个称为名称处理的特殊功能。 Python没有真正的私有属性。相反，Python通过尝试隐藏“私有”属性来实现。这是通过将属性名称与类名称混合在一起来实现的。该错误表明您正在尝试访问其定义以外的类的__item。给定以下类：

class MyObject:
    def __init__(self):
        self.__private = object()

   def get_private(self):
       return self.__private

__private实际上存储为_MyObject__private。

obj = MyObject()
assert obj._MyObject__private is obj.get_private()

如上所述，在类上定义的函数范围之外，仍然可以访问该属性。您只需要知道该怎么称呼。

这意味着，如果您尝试从另一个类（例如子子类）访问此类属性，则可能会出错。 Python不知道您的意思是访问另一个类的“私有”属性，因此该名称将与当前类混淆。例如。

class MyChild(MyObject):
    def swap_private(self, replacement):
        old = self.get_private() 
        # works! get_private is defined on MyObject and so fetches _MyObject__private
        self.__private = replacement 
        # silent error! Would actually store replacement in _MyChild__private
        return old


def set_private(obj, replacement):
    obj.__private = replacement
    # silent error! This function is not defined on a class and so just tries to directly
    # access `__private`

简单的解决方案是除非绝对必要，否则不要使用双下划线名称。如果要将属性标记为私有，则只需使用一个下划线。

AttributeError：'Item'对象没有属性'_Item__name'

1 个答案: