You want to avoid interfering with this attribute. There is no reason to do any kind of stubbing manually - you want to get out of the way and let it do what it usually does. If it behaves like attributes usually do, everything will work correctly.
The correct implementation is therefore to special-case the __objclass__ attribute in your __getattr__ function and throw an AttributeError.
def __getattr__(self, name):
if name == "__objclass__":
# Do something with "name" (by passing it to a server)
This way it will behave the same way as it would in a class that has no __getattr__: The attribute is considered non-existant by default, until it's assigned to. The __getattr__ method won't be called if the attribute already exists, so it can be used without any issues:
>>> obj = some_class()
>>> hasattr(obj, '__objclass__')
>>> obj.__objclass__ = some_class