I want to override my Python class's __getattribute__ and __setattr__ methods. My use case is the usual one: I have a few special names that I want to handle, and I want the default behavior for anything else. For __getattribute__, it seems that I can request the default behavior simply by raising AttributeError. However, how can I achieve the same in __setattr__? Here is a trivial example, implementing a class with immutable fields "A", "B", and "C".
class ABCImmutable(SomeSuperclass):
def __getattribute__(self, name):
if name in ("A", "B", "C"):
return "Immutable value of %s" % name
else:
# This should trigger the default behavior for any other
# attribute name.
raise AttributeError()
def __setattr__(self, name, value):
if name in ("A", "B", "C"):
raise AttributeError("%s is an immutable attribute.")
else:
# How do I request the default behavior?
???
What goes in place of the question marks? With old-style classes, the answer was apparently self.__dict__[name] = value, but documentation indicates that this is wrong for new-style classes.
It's
super(ABCImmutable, self).__setattr__(name, value)
in Python 2, or
super().__setattr__(name, value)
in Python 3.
Also, raising AttributeError is not how you fall back to the default behavior for __getattribute__. You fall back to the default with
return super(ABCImmutable, self).__getattribute__(name)
on Python 2 or
return super().__getattribute__(name)
on Python 3.
Raising AttributeError skips the default handling and goes to __getattr__, or just produces an AttributeError in the calling code if there's no __getattr__.
See the documentation on Customizing Attribute Access.