class ilist(list):

    def __init__(self,dft=None,r=list()):

        super(ilist, self).__init__(r)

        #list.__init__(self,r)

        self.dft=dft

    def __getitem__(self,n):

        while len(self) <= n:

            self.append(self.dft)

        return super(ilist, self).__getitem__(n)

x=ilist(0)

print x[4]

print x

x[0]=10

a=x[0]+x[1]

print a

>>>

0

[0, 0, 0, 0, 0]

10

class ilist(list):

    def __init__(self,dft=None,r=list()):

        list.__init__(self,r)

        self.dft=dft

    def __getitem__(self,n):

        while len(self) <= n:

            self.append(self.dft)

        for i,v in enumerate(self):

            if i==n:

                return v