Extension type inherit from Python int

[Mathias Enzensberger]

Hello,

I am trying to write an extension type that inherits from Pythons int.

Based on the documentation, 
<https://docs.python.org/3/extending/newtypes_tutorial.html#subclassing-other-types> 
this should be possible, but I checked Pythons implementation and the 
struct defining a PyLongObject uses a flexible array to store the limbs 
to support arbitrary large numbers. So having a PyLongObject as first 
member of my own types struct doesn't work because parts of the
ob_digit array would be overwritten by members defined in the subclass 
of the new type that inherits from PyLongObject.

Has anyone already done something like that? Is there some trick to 
work around that issue, or is it simply not possible to inherit from 
PyLongObject?

Thank you,

Mathias