Safer attribute suggestion for classes with custom "bad" `dir` · Issue #139933 · python/cpython · GitHub

Feature or enhancement

Proposal:

Now python suggest for attribute possible in this way:

        obj = exc_value.obj
        try:
            try:
                d = dir(obj)
            except TypeError:  # Attributes are unsortable, e.g. int and str
                d = list(obj.__class__.__dict__.keys()) + list(obj.__dict__.keys())
            d = sorted([x for x in d if isinstance(x, str)])
            hide_underscored = (wrong_name[:1] != '_')
            if hide_underscored and tb is not None:
                while tb.tb_next is not None:
                    tb = tb.tb_next
                frame = tb.tb_frame
                if 'self' in frame.f_locals and frame.f_locals['self'] is obj:
                    hide_underscored = False
            if hide_underscored:
                d = [x for x in d if x[:1] != '_']
        except Exception:
            return None

However, the obj may has no attribute "__dict__" if it has the attribute "__slots__". So list(obj.__class__.__dict__.keys()) + list(obj.__dict__.keys()) is not safe. And the class must have the attribute "__name__" that the object of the class cannot get.
In fact, the object.__dir__ is safer, it can exactly find all of the attribute that can be get with object.__getattribute__. So I think that we can change the way by using this way.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

Please provide context, both in the title and issue body, I had to go grep the lines you provided.

Please provide context, both in the title and issue body, I had to go grep the lines you provided.

traceback.py at line 1635-1653

Looking at the discussion on the recent PR which added these lines, #131001, the current approach was preferred.

Looking at the discussion on the recent PR which added these lines, #131001, the current approach was preferred.

Yes. However, object.__dir__ is unchangable and it won't sort the list, so it cannot raise TypeError:

>>> class MyClass:
...     pass
...
>>> a = MyClass()
>>> a.__dict__[1] = 1
>>> object.__dir__(a)
[1, '__module__', '__firstlineno__', '__static_attributes__', '__dict__', '__weakref__', '__doc__', '__new__', '__repr__', '__hash__', '__str__', '__getattribute__', '__setattr__', '__delattr__', '__lt__', '__le__', '__eq__', '__ne__', '__gt__', '__ge__', '__init__', '__reduce_ex__', '__reduce__', '__getstate__', '__subclasshook__', '__init_subclass__', '__format__', '__sizeof__', '__dir__', '__class__']

And then d = sorted([x for x in d if isinstance(x, str)]) make sure that the 1 in the list will be ignore.
This way is more powerful.

There is indeed an "issue":

class A:
    __slots__ = ()
    def __dir__(self):
        return [1, "abc"]

If you have:

>>> a = A()
>>> a.<TAB>

then there won't be any completion suggestion because we're catching the AttributeError and returning None directly. I'm considering this as a bug because we're not trying hard enough here to get the attributes. OTOH, I need to check if object.__dir__ is safe to call (that is, if this wouldn't trigger side-effects).

It seems that it is normal with object.__dir__:

>>> class A:
...     __slots__ = ()
...     def __dir__(self):
...         return [1, "abc"]
...
>>> a = A()
>>> object.__dir__(a)
['__module__', '__firstlineno__', '__slots__', '__dir__', '__static_attributes__', '__doc__', '__new__', '__repr__', '__hash__', '__str__', '__getattribute__', '__setattr__', '__delattr__', '__lt__', '__le__', '__eq__', '__ne__', '__gt__', '__ge__', '__init__', '__reduce_ex__', '__reduce__', '__getstate__', '__subclasshook__', '__init_subclass__', '__format__', '__sizeof__', '__class__']

It's not just for this specific case. I need to know what happens in C for that. Now, I've confirmed that object.__dir__ is simply the default dir() so nothing fancy should happen. However, what is concerning is that if dir() is failing, then object.__dir__(x) has no meaning because a failing dir() means a custom dir(), which in turn means that the default one is not good.

Therefore, I think we should just give up on using __dict__ here and only rely on the class attributes.

And then I will test for this object:

#include <nanobind/nanobind.h>
#include <nanobind/stl/string.h>
#include <nanobind/stl/vector.h>
#include <nanobind/stl/shared_ptr.h>
#include <nanobind/stl/map.h>
#include <nanobind/stl/unordered_set.h>

class NonPyObject {
};

class TargetObject {
public:
    TargetObject(int a, int b): a(a), b(b) {
        
    }
    int add() {
        return a+b;
    }
private:
    int a;
    int b;
};

namespace nb = nanobind;
NB_MODULE(targetobject, m) {
    nb::class_<TargetObject>(m, "TargetObject")
        .def(nb::init<int, int>())
        .def("add", &TargetObject::add)
        .def("__dir__", [](const TargetObject &self){
            return NonPyObject();
    });
};

It's not just for this specific case. I need to know what happens in C for that. Now, I've confirmed that object.__dir__ is simply the default dir() so nothing fancy should happen. However, what is concerning is that if dir() is failing, then object.__dir__(x) has no meaning because a failing dir() means a custom dir(), which in turn means that the default one is not good.

Therefore, I think we should just give up on using __dict__ here and only rely on the class attributes.

The object.__dir__ won't sort the result. This is the biggest difference.

It doesn't matter. As you can see, object.__dir__(a) is lacking "abc". In case object.__dir__(a) actually outputs something that was not meant to be returned by the custom __dir__, it will be worse. So relying on the default behavior of __dir__ is not really a better idea IMO. I prefer to have missing suggestions rather than having incorrect ones.

In fact, a.__dir__() is also unsorted. So, we can try to just call it. What will sort the result is only dir(), unless the code sorted the result before in __dir__

Oh, I thought there was some callback for the __dir__ method. Ok, yes, let's just call __dir__. Thanks for that.

gh-139933: correctly suggest attributes for classes with a custom `__…

[3.14] pythongh-139933: correctly suggest attributes for classes with…

[3.14] gh-139933: correctly suggest attributes for classes with a cus…

[3.13] pythongh-139933: correctly suggest attributes for classes with…

[3.13] gh-139933: correctly suggest attributes for classes with a cus…

pythongh-139933: correctly suggest attributes for classes with a cust…

Safer attribute suggestion for classes with custom "bad" `dir` · Issue #139933 · python/cpython · GitHub

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Safer attribute suggestion for classes with custom "bad" dir #139933

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Safer attribute suggestion for classes with custom "bad" __dir__ #139933

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Feature or enhancement

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StanFromIreland commented on Oct 11, 2025

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Safer attribute suggestion for classes with custom "bad" `dir` · Issue #139933 · python/cpython · GitHub

Safer attribute suggestion for classes with custom "bad" dir #139933