Abort from type checking mismatch between `_suggestions__generate_suggestions_impl` and `_Py_CalculateSuggestions`

[devdanzin]

Crash report

What happened?

This is a silly one: _suggestions__generate_suggestions_impl, which checks whether the candidates is a list or subclass, calls _Py_CalculateSuggestions, which checks whether candidates is an exact list instance with an assert that fails if _suggestions._generate_suggestions receives an instance of a list subclass.

import _suggestions
class L(list): pass
_suggestions._generate_suggestions(L(), "")
python: Python/suggestions.c:132: _Py_CalculateSuggestions: Assertion `PyList_CheckExact(dir)' failed.
Aborted (core dumped)

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows, Linux

Output from running 'python -VV' on the command line:

Python 3.14.0a6+ (heads/main:be2d2181e62, Mar 31 2025, 07:30:17) [GCC 11.4.0]

Linked PRs

• gh-131936: Relax assertion in _Py_CalculateSuggestions  #131943
• gh-131936: Strengthen check in _suggestions._generate_suggestions #131945
• [3.13] gh-131936: Strengthen check in _suggestions._generate_suggestions (GH-131945) #131949

[ZeroIntensity]

I'm pretty sure we can relax that assertion. I don't see why it has to be exactly a list.

[vstinner]

Fixed by change 511d344.