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load_setup_py_data() executes setup.py in the conda-build process. setup.py prepends "." to sys.path, so the source tree's unbuilt zstandard package later shadows the zstandard bindings that conda-package-handling imports for .conda support. conda-build then fails with "Didn't recognize extension for file '...conda'". Read the version from c-ext/python-zstandard.h with load_file_regex() instead.
cibuildwheel installs the test-groups packages unlocked, so it picked up the latest mypy, which now depends on ast-serialize. ast-serialize has no wheels for musllinux_1_1 or musllinux s390x, and building it from source needs a Rust toolchain the containers don't have, failing those wheel jobs before any test ran. Move the test suite's dependencies into a new "test" dependency group, have "dev" include it plus mypy, and point cibuildwheel at "test".
On Apple Silicon runners Homebrew installs into /opt/homebrew, which isn't on the compiler's default search paths, so the --system-zstd build failed with "'zdict.h' file not found". Pass Homebrew's include and lib directories explicitly, and build for arm64 only since Homebrew's libzstd is not universal2.
test_stream_source_readinto intermittently fails on macos-26-intel runners with DeadlineExceeded: a single example took 31s against the 20s deadline, then 18s on hypothesis's rerun, which hypothesis reports as a FlakyFailure. The timing depends on runner load, not on the code under test, so don't enforce a deadline in the ci profile, as the expensive profile already does.
PyO3 0.29 is the first release that supports Python 3.15. Port the Rust backend to the APIs renamed or removed since 0.25: PyObject becomes Py<PyAny>, downcast*() becomes cast*(), allow_threads() becomes detach() and assume_gil_acquired() becomes assume_attached(). Py::from_borrowed_ptr() is deprecated, so build the parent reference in ZstdBufferWithSegments.segments() with a safe conversion instead of a raw pointer cast.
Build cp315 and cp315t wheels and add 3.15 and 3.15t to the test and typing CI matrices. Like 3.14, Linux wheels for 3.15 are built with manylinux_2_28 and musllinux_1_2 only. Add the Python 3.15 trove classifier and list 3.15 as supported in the docs.
This was referenced Oct 16, 2026
pylaterreur
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Oct 16, 2026
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Thanks for this. I built and tested this on Linux x86_64 with GitHub's CPython 3.15.0 and 3.15.0t builds, the ones setup-python installs. I used test.yml's settings: uv 0.8.11, ZSTD_WARNINGS_AS_ERRORS=1, ZSTD_SLOW_TESTS=1, the hypothesis ci profile and PYTHONDEVMODE=1, with -n 2.
| C | CFFI | Rust (PyO3 0.29.3) | wheel from uv build, tested like cibuildwheel (C / CFFI) |
|
|---|---|---|---|---|
| 3.15.0 | 292 passed | 266 passed, 26 skipped | 291 passed, 1 failed | 248 passed, 44 skipped / 224 passed, 68 skipped |
| 3.15.0t | 292 passed | 266 passed, 26 skipped | 291 passed, 1 failed | 248 passed, 44 skipped / 224 passed, 68 skipped |
The Rust failure is test_optimize, which also fails on main. On 3.15.0t, the GIL stays disabled after importing the C or CFFI backend. No code changes were needed.
Two things in CI:
wheel.ymlstill runs cibuildwheel 4.1.0, which builds the macOS and Windows cp315/cp315t wheels against 3.15.0b2. Your fork's macos (cp315, arm64) job showsPython 3.15.0b2 (v3.15.0b2:94a64bbc6ce, ...)and windows (cp315, win_amd64) showsPython 3.15.0b2 (tags/v3.15.0b2:94a64bb, ...). cibuildwheel 4.3.1 builds against the final 3.15.0. I opened zydo#1 against your branch with that bump. A run of it builds and tests the macOS and Windows cp315/cp315t wheels against the final 3.15.0.- The 3.15t jobs in test.yml don't run on a free-threaded Python, and neither do the existing 3.13t/3.14t jobs. uv 0.8.11 skips the free-threaded interpreter from setup-python, so your fork's test (ubuntu-24.04, 3.15t, x64) used
/usr/bin/python3(3.12.3). The 3.15.0t results above come from the real free-threaded build. #360 fixes this on main. In a run of it, the 3.13t/3.14t jobs usepython3.13t/python3.14tand pass.
Prepared with the help of Claude Code.
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Adds Python 3.15 support:
cp315andcp315twheels on Linux, macOS and Windows. Like 3.14, Linux wheels usemanylinux_2_28andmusllinux_1_2only.No C, CFFI or Python code changes were needed. On every 3.15 and 3.15t test job, the C and CFFI backends pass in full, and the Rust backend (with the PyO3 0.29 upgrade) has only the
test_optimizefailure it also has onmain.Refs #354. This makes CI build the 3.15 wheels; publishing them to PyPI still needs a release.
Depends on #356 (PyO3 0.29, which depends on #358); only the last commit belongs to this PR.
All workflows pass on the fork: https://github.com/zydo/python-zstandard/actions?query=branch%3Apython-3.15