Python 'MyClass' 对象没有属性 '__getitem__'
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'MyClass' object has no attribute '__getitem__'
提问by floatingpurr
I have a class like this one:
我有一堂这样的课：
class MyClass(object):
def __init__(self, id, a, b, c):
self.myList = []
self.id = id
self.a = a
self.b = b
self.c = c
def addData(self, data):
self.myList.append(data)
In my main code, I create a list of MyClass instances called myClassList. In a line I have to check if an item with a given idalready exists. I do it in this way:
在我的主代码中，我创建了一个名为myClassList. 在一行中，我必须检查具有给定的项目是否id已经存在。我是这样做的：
id = 'foo' # in real code is set dynamically
recent_item = next( (item for item in myClassList if item['id'] == id), None )
The second line in that code gives this error:
该代码中的第二行给出了这个错误：
'MyClass' object has no attribute
'__getitem__'
“MyClass”对象没有属性
'__getitem__'
How can I fix?
我该如何解决？
采纳答案by hiro protagonist
itemis not a dictionary but a class so it has different syntax for accessing members. Access idthis way instead:
item不是字典而是一个类，因此它具有不同的访问成员的语法。以id这种方式访问：
item.id
回答by Anand S Kumar
Like the error suggests, you can only use subscript on class instances, if the class defines a __getitem__()instance method.
就像错误提示的那样，如果类定义了__getitem__()实例方法，则只能在类实例上使用下标。
As idis an attribute of the instance, you should use - item.idinstead of item['id'].
作为id实例的一个属性，您应该使用 -item.id而不是item['id']。
Example -
例子 -
recent_item = next( (item for item in myClassList if item.id == id), None )
回答by Anbarasan
idis an attribute of MyClass instance, you have to access it as item.id
id是 MyClass 实例的一个属性，你必须访问它 item.id
recent_item = next( (item for item in myClassList if item.id == id), None )
回答by Padraic Cunningham
If you actually wanted to be able to access your attributes using inst["attr"]and to explain your error, you would need to add a __getitem__to you class:
如果您确实希望能够使用inst["attr"]并解释您的错误来访问您的属性，则需要__getitem__向您的类中添加一个：
class MyClass(object):
def __init__(self, id, a, b, c):
self.myList = []
self.id = id
self.a = a
self.b = b
self.c = c
def addData(self, data):
self.myList.append(data)
def __getitem__(self, item):
return getattr(self, item)
回答by Aidan Hoolachan
As others have noted, you can simply use
正如其他人所指出的，您可以简单地使用
item.id
However, sometimes you do need to use this syntax if you are accessing a field dynamically:
但是，如果您要动态访问字段，有时确实需要使用此语法：
item[dynamicField]
In that case, you can use the __getitem__() syntax as Anand suggested, however it is safer to use python's wrapper for __getitem__:
在这种情况下，您可以按照 Anand 的建议使用 __getitem__() 语法，但是使用 python 的 __getitem__ 包装器更安全：
getattr(item, dynamicField)
