version: support importing under sub-interpreters - #343
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Python 3.12+ won't load single-phase C extensions inside a sub-interpreter. Convert _version to multi-phase init so it imports there, and declare it safe to run with a per-interpreter GIL. _version has no state, so this is a mechanical conversion. Since lz4/__init__ imports it, this is also what lets `import lz4` work in a sub-interpreter. No API change, and older Python versions are unaffected.
jinh-labs
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July 7, 2026 11:31
This was referenced Jul 27, 2026
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What
Make
import lz4work inside a sub-interpreter. Python 3.12+ won't import single-phase C extensions in a sub-interpreter, andlz4/__init__.pyimports_version— so todayimport lz4fails there withImportError: module _version does not support loading in subinterpreters. This converts_versionto multi-phase init and declares it safe under a per-interpreter GIL.Part of #345 - multi-phase init for the
_versionmodule (see also #340_frame, #341_block, #342_stream).Relationship to the other PRs
Part of a series making the whole package sub-interpreter-compatible: #340 (frame), #341 (block), #342 (stream), and this one (
_version).These are independent and can merge in any order. They touch different files and don't conflict. But this PR is the gate: because
import lz4(and therefore anyimport lz4.frame/lz4.block/lz4.stream, which import the parent package first) goes through_version, the normal import paths stay blocked in a sub-interpreter until this one lands. With all four in, the whole package loads and round-trips in an isolated, own-GIL sub-interpreter.Why it's safe
_versionhas no module state and just wraps the reentrant LZ4 version calls, so it is safe even in fully isolated interpreters. This is a mechanical conversion.Compatibility
No API change. The new declaration is guarded for Python 3.12+, so builds on older Python are unaffected.
Testing
import lz4succeeds in an isolated, own-GIL sub-interpreter.Refs: PEP 489, Isolating Extension Modules