René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`__lazy_import__` crashes with user-defined filters","articleBody":"# Crash report\n\n### Bug description:\n\nThis crashes from an assertion error, only when `__lazy_import__` is called directly:\n\n```python\nimport sys\n\ndef li_filter(importing_module: str, imported_module: str, fromlist: tuple[str, ...]) -\u003e bool:\n    return False\n\nsys.set_lazy_imports_filter(li_filter)\n\n__lazy_import__('wave')\n```\n\nMoved from https://github.com/LazyImportsCabal/cpython/issues/45 (couldn't have transferred it).\n\nThe compiler would always put a `LOAD_CONST (None)` before any `IMPORT_NAME` for imports without `from`, which is why this crash never happens in a regular `lazy import`.\n\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\n_No response_\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-144852\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/johnslavik","@type":"Person","name":"johnslavik"},"datePublished":"2026-02-15T21:37:15.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/144851/cpython/issues/144851"}