python override dot syntax functionality in a class method

Question

is this possible? I want to assign a value to a custom dictionary using <class_name>.<attribute_name> syntax.

here's an example:

class Foo:
    def __init__(self):
        self.__values__ = {}
    def add_a_value_using_dot_syntax(self, index, value): # what should this be?
        self.__values__[index] = value

bar = Foo()
bar.baz = 'hello'

print(bar.baz) # hello
print(bar.__values__) # {'baz': 'hello'}

I know that this can be done with bracket syntax by overriding __setitem__ but it doesn't seem to work for dot syntax..

Thanks

Answer 1

You'd need to override __getattr__ and __setattr__, but since these are fundamental to how the class works, you'd need some extra logic, and there's an enormous minefield of potentially undefined behavior. I think you'd want

class Foo:
    def __init__(self):
        self.__values__ = {}
        super().__init__()

    def __setattr__(self, name, value):
        if name == '__values__':
            self.__dict__['__values__'] = value
            return
        try:
            self.__getattr__(name)
        except AttributeError:
            self.__values__[name] = value
        return super().__setattr__(name, value)

    def __getattr__(self, name):
        if name == '__values__':
            return self.__dict__['values']
        try:
            return super().__getattr__(name)
        except AttributeError:
            try:
                return self.__values__[name]
            except KeyError:
                raise AttributeError

This is extremely evil/cursed, and should never be done.