Safer attribute suggestion for classes with custom "bad" `__dir__`

[Locked-chess-official]

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

• gh-139933: correctly suggest attributes for classes with a custom __dir__ #139950

[StanFromIreland]

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

[Locked-chess-official]

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

[StanFromIreland]

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

[Locked-chess-official]

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.

[picnixz]

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).