How to add new attributes to struct_spwd type while preserving its original attributes?

How to add new attributes to struct_spwd type while preserving its
original attributes?

Python has spwd module to interact with shadow password file.
You must be root to use spwd module.
>>> import spwd;
>>> a = spwd.getspnam('bin')
>>> type(a)
<class 'spwd.struct_spwd'>
>>> a.__gt__
<method-wrapper '__gt__' of spwd.struct_spwd object at 0x7fd017641b80>
Now I want to add a new attribute to object 'a' (or class 'struct_spwd').
How do I do that?
Inheritance does not work.
import spwd
class Abc(spwd.struct_spwd):
pass
I got "TypeError: type 'spwd.struct_spwd' is not an acceptable base type".
Adding dynamic attributes to object does not work.
import spwd
a = spwd.getspnam('bin')
a.new_attribute = lambda: print('hello world')
I got "AttributeError: 'spwd.struct_spwd' object has no attribute
'new_attribute'".
Using delegation could work, though. But I want to preserve its original
attributes.
import spwd
class Abc(object):
def __init__(self, struct_spwd):
self.struct_spwd = struct_spwd
def __getattribute__(self, name):
if name=='new_attribute':
print('hello world')
else:
self.struct_spwd.__getattribute__(name)
a = spwd.getspnam('bin')
b = Abc(a)
b.new_attribute
b.__gt__
I got "RuntimeError: maximum recursion depth exceeded in comparison".
Any idea? Or should I use other ways to achieve my goal? Thx.