bug or feature?

[Mettler]

Hi people!

I have been playing around with python a little and came across this:
consider the following code in Python3

class THING:
    def __init__(self):
        
        self.number=10
        self.valueDict={
            0: self.number
        }
    def __getitem__(self,index):
        return self.valueDict[index]
    
    def __setitem__(self,index,newVal):
        if index==0:
            self.number=newVal

does not work consistently:

Output:
IN:a=THING()

IN:a[0]
Out: 10

IN:a[0]=9

IN:a[0]
Out: 10

The dictionary seems to address a different variable but it is not so:

class THING:
    def __init__(self):
        
#      self.number=10
        self.valueDict={
            0: self.number
        }
    def __getitem__(self,index):
        return self.valueDict[index]
    
    def __setitem__(self,index,newVal):
        if index==0:
            self.number=newVal

results after initialisation are:

Error:
AttributeError: 'THING' object has no attribute 'number'

my Workaround is:

class THING:
    def __init__(self):
        
        self.number=10
        self.valueDict={
            0: lambda: self.number
        }
    def __getitem__(self,index):
        return self.valueDict[index]()
    
    def __setitem__(self,index,newVal):
        if index==0:
            self.number=newVal

Output:
IN:e=THING()

IN:e[0]
Out: 10

IN:e[0]=9

IN:e[0]
Out: 9

Now why is that, or better what is the purpose? ...and I know I could have just used a map for __setitem__ as well

Cheers