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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 id already exists. I do it in this way:

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:
  
'MyClass' object has no attribute '__getitem__'
How can I fix?
                ...you could implement __getitem__! Alternatively, use item.id instead of item['id']. Note also that you're assigning self.id = a, which is likely not what you intended, and aren't compliant with the style guide.
– jonrsharpe
                Aug 4, 2015 at 10:45
item is not a dictionary but a class so it has different syntax for accessing members. Access id this way instead:
item.id
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:
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)
However, sometimes you do need to use this syntax if you are accessing a field dynamically:
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__:
getattr(item, dynamicField)
                Sorry to beat a dead bush, but I think it would be correct to call it a property in this case? stackoverflow.com/a/7374831/6743506
– Bryant James
                Dec 15, 2017 at 14:43
Like the error suggests, you can only use subscript on class instances, if the class defines a __getitem__() instance method.
As id is an attribute of the instance, you should use - item.id instead of item['id'] .
Example -
recent_item = next( (item for item in myClassList if item.id == id), None )
        
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