How to implement __setattr__ without infinite recursion

[pagano.paganino]

@jimmo into the issue : py: object base class doesn't implement __setattr__ and __delattr__ #2755 i have already implemented this, can be this reuse?

[Jongy]

@jimmo These are clever solutions but a naive Python programmer would expect to use object.__setattr__() to break the recursion. Would implementing this be a major problem?

Oh yeah, wholeheartedly agree!! Just got distracted by the puzzle, but I have already started doing exactly that (implementing object.__setattr__).

Well, where's the PR?

I wrote a piece of code today that worked nicely in CPython. It took a while to learn this object.__setattr__ trick. Anyway, I was quite sad when I got the first "AttributeError: 'super' object has no attribute '__setattr__'" exception.

Lucky I found this thread! I feel more okay now knowing that I wasn't fighting Python for nothing. Something's really missing.

I'd be happy to add it if you haven't got to it yet.

[Jongy]

Okay I patched something quick and it seems to work. It's late so I'll tidy it up and open a PR tomorrow.
I added an "object.__setattr__" function that basically does "mp_map_lookup(&self->members, attr, MP_MAP_LOOKUP_ADD_IF_NOT_FOUND)->value = value;".

The following code now works:

Code: Select all

class X(object):
    def __init__(self):
        object.__setattr__(self, "y", 5)

    def __setattr__(self, attr, value):
        print(attr, "=", value)

An X object is created, nothing is printed and it has a "y" attribute.

"super(X, self).__setattr__" doesn't work yet though If I define it as a static method then object.__setattr__ works but the "super" trick doesn't.
If I remove the static method, then "super(X, self).__setattr__" works but object.__setattr__ is now rejected with "TypeError: argument should be a 'object' not a 'X'".

[Jongy]

See https://github.com/micropython/micropython/pull/5404.

[pagano.paganino]

https://github.com/micropython/micropython/issues/2755
See this comment: https://github.com/micropython/micropyt ... -270940142