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__lazy_import__ crashes with user-defined filters #144851

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__lazy_import__ crashes with user-defined filters#144851
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johnslavik
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3.15bugs and security fixesinterpreter-core(Objects, Python, Grammar, and Parser dirs)release-blockertype-crashA hard crash of the interpreter, possibly with a core dump

Description

@johnslavik
johnslavik
opened on Feb 15, 2026

Crash report

Bug description:

This crashes from an assertion error, only when __lazy_import__ is called directly:

import sys

def li_filter(importing_module: str, imported_module: str, fromlist: tuple[str, ...]) -> bool:
    return False

sys.set_lazy_imports_filter(li_filter)

__lazy_import__('wave')

Moved from LazyImportsCabal#45 (couldn't have transferred it).

The 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.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

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Activity

  1. johnslavik
    added
    interpreter-core(Objects, Python, Grammar, and Parser dirs)
    type-crashA hard crash of the interpreter, possibly with a core dump
    on Feb 15, 2026
  2. johnslavik
    self-assigned this
    on Feb 15, 2026
  3. johnslavik
    added
    3.15bugs and security fixes
    on Feb 21, 2026

  4. johnslavik commented on Mar 1, 2026

    @johnslavik
    johnslavik
    on Mar 1, 2026
    MemberAuthor

    This hard crashes (segfaults) in the release build, so I'm marking this as a release blocker.

  5. johnslavik
    added
    release-blocker
    on Mar 1, 2026
  6. github-project-automation
    added this to Release and Deferred blockers 🚫on Mar 1, 2026
  7. github-project-automation
    moved this to Todo in Release and Deferred blockers 🚫on Mar 1, 2026

  8. johnslavik commented on Mar 1, 2026

    @johnslavik
    johnslavik
    on Mar 1, 2026
    MemberAuthor

    cc @pablogsal @DinoV @Yhg1s @brittanyrey

  9. Yhg1s
    added a commit that references this issue on Mar 2, 2026

    gh-144851: Fix `__lazy_import__` crash with user-defined filters (#14…

    8bcb3ea

  10. johnslavik commented on Mar 2, 2026

    @johnslavik
    johnslavik
    on Mar 2, 2026
    MemberAuthor

    Thanks @Yhg1s for the quick review!

  11. johnslavik
    closed this as completedon Mar 2, 2026
  12. github-project-automation
    moved this from Todo to Done in Release and Deferred blockers 🚫on Mar 2, 2026
  13. johnslavik
    added a parent issue on Apr 14, 2026
  14. ljfp
    added a commit that references this issue on Apr 25, 2026

    pythongh-144851: Fix `__lazy_import__` crash with user-defined filters (

    80e8f88
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3.15bugs and security fixesinterpreter-core(Objects, Python, Grammar, and Parser dirs)release-blockertype-crashA hard crash of the interpreter, possibly with a core dump

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