Reconsider gh-88915 changes rlcompleter since exceptions in descriptors cause auto completion to fail

Bug report

Bug description:

In BPO 44752 (#88915), it was reported that tab completions execute @property getters. This was fixed in two stages:

bpo-44752: Make rlcompleter not call @property methods #27401: no longer call property getters
bpo-44752: Make rlcompleter not call @property methods #27401: No longer catch errors raised by a call to getattr.

It looks like when investigating/solving this issue, it was unconsidered that @property isn't the only case where calling an underlying method might be undesirable. For example, in the NVDA project, we have the following non-data descriptor (simplified for clarity):

class Getter:
    def __init__(self, fget):
        self.fget = fget

    def __get__(self, instance, owner):
        if isinstance(self.fget, classmethod):
            return self.fget.__get__(instance, owner)()
        elif instance is None:
            return self
        return self.fget(instance)


class SomeClass:
    @Getter
    def some_prop(self):
        raise NotImplementedError

If we'd create an instance of SomeClass and try to autocomplete, rlcompleter.Completer.attr_matches would fail with the NotImplementedError raised by some_prop

I'd propose one of the following:

Restore the try/except removed in bpo-44752: Make rlcompleter not call @property methods #27401
Create abstract classes for descriptors in _collections_abc (e.g. ImplementsGet, ImplementsSet, ImplementsDelete) and in rlcompleter, rather than checking for isinstance(obj, property), use isinstance(obj, ImplementsGet). This might cause false positives for method descriptors though.

CPython versions tested on:

3.11

Operating systems tested on:

Windows

Linked PRs

@jdevries3133

@jdevries3133 since you worked on this code, it would be most valuable if you could share your opinion on this.

@LeonarddeR

Hello,
if the class' property is created with Cython (0.29 or 3.0.8), it also fails the isinstance(..., property) test mentioned by @LeonarddeR .
So rlcompleter also fails on these cython classes when the property raises an exception.

I've set up a small reproducible example here: https://github.com/Demi-Lune/cython_property_is_attribute.
This example worked fine with python3.8.

For example:

# file my_cython_class.pyx
cdef class B:
    cdef int _size
    def __init__(self):
        self._size = 42

    @property
    def size(self):
        return self._size
    @size.setter
    def size(self, size):
        self._size = size

    @property
    def name(self):
        if self.size != 42:
            raise RuntimeError("B has no name")
        else:
            return "forty-two"

produces:

>>> from mytest.my_cython_class import B
>>> isinstance(B.size, property)
False
>>> B.size
<attribute 'size' of 'mytest.my_cython_class.B' objects>
>>> b.size
42
>>> b.<TAB><TAB>
b.name  b.size
>>> b.size = 0
>>> b.<TAB><TAB>
# no completion, because property b.size raises an exception

So I'm in favor of @LeonarddeR 's first suggestion (Restore the try/except).

A reproducer using only builtins:

>>> mv = memoryview(b"abc")
>>> mv.release()
>>> mv.<TAB>
# no completion because mv.shape raises an exception

pythongh-112821: Fix rlcompleter failures on objects with descriptors

gh-112821: Fix rlcompleter failures on objects with descriptors (#149577

[3.15] gh-112821: Fix rlcompleter failures on objects with descriptors (

[3.14] gh-112821: Fix rlcompleter failures on objects with descriptors (

[3.13] gh-112821: Fix rlcompleter failures on objects with descriptors (

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Reconsider gh-88915 changes rlcompleter since exceptions in descriptors cause auto completion to fail #112821

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Reconsider gh-88915 changes rlcompleter since exceptions in descriptors cause auto completion to fail #112821

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Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

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LeonarddeR commented on Dec 7, 2023

JeanDidierGaraud commented on Mar 20, 2024

mdboom commented on May 8, 2026

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