feat: pyemscripten platform tag (PEP 783), 314.0a1, pyodide-eol flag, and maintenance updates (#2812)
* Use `pyodide config get emscripten_dir` * Update constraints * Updates for `pyemscripten` platform tag * Weird constraints stuff... * Revert "Weird constraints stuff..." This reverts commit 4bd785de872269c0b27362ee800f17288b2b4789. * Add some special constraints for pyodide * Wheel pyemscripten collision * Put delocate back in constraints (not needed tho) * Drop Pyodide 0.27.7 (cp312-pyodide_wasm32) * Add Pyodide 314.0.0a1 (cp314-pyodide_wasm32) * Delete no-longer-needed Pyodide 312 constraints * Update Pyodide 313 and 314 constraints * Add back prerelease stuff and update tests * Fix `test_pyodide_on_windows` * Update and fix tests some more * Also enable pyodide-prerelease in GHA sample build * Update tests yet again (`SINGLE_PYTHON_VERSION` changes) * Add a Pyodide-specific maintenance guide * Add suggestions from Hood and Gyeongjae Co-Authored-By: Hood Chatham <roberthoodchatham@gmail.com> Co-Authored-By: Gyeongjae Choi <def6488@gmail.com> * Add "Last updated: May 2026" to Pyodide document * Add a Pyodide EOL filter * Fix typo * Update maintenance docs about EoL Pyodide * Add Pyodide 312 constraints back * Update Pyodide 313 and 314 constraints * Remove "experimental" note about Pyodide * Remove another experimental Pyodide sentence * Add docs about the `pyodide-eol` enable option --------- Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com> Co-authored-by: Gyeongjae Choi <def6488@gmail.com> Co-authored-by: Henry Schreiner <henryfs@princeton.edu>
This commit is contained in:
agriya khetarpal
co-authored by
Hood Chatham
Gyeongjae Choi
Henry Schreiner
Hood Chatham
Gyeongjae Choi
Henry Schreiner
parent
542335fb4a
commit
d2c0e59833
@@ -0,0 +1,113 @@
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# Maintaining Pyodide support
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Last updated: May 2026
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This page describes how to update cibuildwheel's Pyodide platform code when either:
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- a new Pyodide alpha release arrives with support for a new [PyEmscripten Platform](https://pyodide.org/en/latest/development/abi.html) (which is tied to updates in Emscripten and CPython versions, compiler/linker flags, and so on), or
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- when that alpha release graduates to a stable one.
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## Background
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Pyodide has three types of releases that matter to cibuildwheel:
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- **Stable** – the most recent full Pyodide release (e.g., `0.29.x` / cp313). This is enabled by default with no special `CIBW_ENABLE` flag needed.
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- **Prerelease** – an alpha/beta/rc Pyodide release that uses the _next_ CPython version (e.g., `314.0.0a1` / cp314). Users must opt in with `CIBW_ENABLE: pyodide-prerelease` to build against this version. This may or may not be available at any given time, depending on the Pyodide release cycle.
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- **End-of-life (EoL)** – older Pyodide stable releases that are no longer the current stable. These are kept available behind `CIBW_ENABLE: pyodide-eol` so that users who still need to build for older Pyodide versions can do so.
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The guards in `cibuildwheel/selector.py` enforce this distinction. The constraints files under `cibuildwheel/resources/` pin the exact tool versions that go with each build.
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---
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## When a new Pyodide prerelease becomes available
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For example, consider a scenario when Pyodide ships a new `315.0.0a1` with cp315 support.
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### 1. Add the new Python configuration
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In `cibuildwheel/resources/build-platforms.toml`, add an entry under `[pyodide]`:
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```toml
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{ identifier = "cp315-pyodide_wasm32", version = "3.15", default_pyodide_version = "315.0.0a1", node_version = "v24" },
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```
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`version` is the CPython version string, `default_pyodide_version` is the Pyodide release to use when the user does not pin one explicitly (use the latest available alpha/beta for a prerelease entry), and `node_version` is the minimum Node.js major required by that Pyodide release — check the [pyodide-build FAQ](https://pyodide-build.readthedocs.io/en/latest/faq.html#what-node-js-version-do-i-need) for a rudimentary idea of what the correct value is.
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### 2. Update the prerelease guards in the selector
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In `cibuildwheel/selector.py`, update the patterns in the `PyodidePrerelease` guards to match the new identifier:
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```python
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if EnableGroup.PyodidePrerelease not in self.enable and fnmatch(
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build_id, "cp315-pyodide_*"
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):
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return False
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```
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### 3. Generate and pin a constraints file
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Run the `update_constraints` `nox` session, which reads `build-platforms.toml` and regenerates all Pyodide constraints files automatically:
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```bash
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nox -s update_constraints
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```
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### 4. Update tests
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Update the unit tests so the new identifier is accepted by the selector with `PyodidePrerelease` enabled and rejected without it. Pyodide-specific integration tests may also need their hardcoded expected-wheel lists extended.
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## When a Pyodide prerelease becomes stable
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Pyodide uses a versioning scheme where the stable release for a given CPython version is named `[PythonMajorMinor].0.0`, so the first stable release shipping cp314 will be **`314.0.0`**. See [pyodide/pyodide#6084](https://github.com/pyodide/pyodide/issues/6084) for a rationale of this versioning scheme.
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### 1. Update the stable entries, and remove (or replace) the prerelease entry
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In `build-platforms.toml`, update the former prerelease entry's `default_pyodide_version` to the new stable release (e.g. `314.0.0`) and remove the prerelease marker from the identifier if present. Remove previous prerelease entries if they are now obsolete, or update them to the next prerelease if one is available. Move the previous stable version behind `pyodide-eol` rather than dropping it outright (see below).
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### 2. Disable or update the prerelease guards
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In `selector.py`:
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- **If a new prerelease is available**: update the `fnmatch` pattern to the next identifier (e.g. `cp315-pyodide_*`) as described above.
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- **If there is no new prerelease**: comment out the `PyodidePrerelease` logic.
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### 3. Update the constraints file
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Run `nox -s update_constraints` to regenerate the constraints file for the newly stable version. If the entry was already in `build-platforms.toml` as a prerelease, its constraints file already exists, and this step just refreshes it against the stable Pyodide release and updates the dependencies' versions.
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### 4. Update tests
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Update the unit tests so the newly stable identifier is accepted by the selector without needing `PyodidePrerelease` in the enable set. Pyodide-specific integration tests may also need their hardcoded expected-wheel lists extended.
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## When an old Pyodide version is to be moved to end-of-life
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When a Pyodide version is superseded by a new stable release, move it behind the `pyodide-eol` enable flag. We want to allow users who still build for older Pyodide ABIs time to upgrade.
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### 1. Add the `pyodide-eol` guard in the selector
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In `cibuildwheel/selector.py`, add (or update) the `PyodideEoL` guard to include the old identifier:
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```python
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if EnableGroup.PyodideEoL not in self.enable and fnmatch(build_id, "cp312-pyodide_*"):
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return False
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```
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### 2. Update tests
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Update the unit tests so the EoL identifier requires `PyodideEoL` to be included in the enable set. The default (no `CIBW_ENABLE`) should exclude it.
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## When an old Pyodide version is to be fully retired
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Retirement is not expected to happen on a routine basis. It is only warranted when the Pyodide ecosystem itself has evolved to the point where an older ABI version is considered obsolete – for example, if the surrounding toolchain, packaging standards, or runtime infrastructure have moved on so substantially that building for the older version no longer makes practical sense. Any retirement is to be discussed and agreed upon by Pyodide maintainers before proceeding.
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### 1. Remove the Python configuration
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Delete the entry from `build-platforms.toml` and remove the `PyodideEoL` guard for that identifier in `selector.py`.
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### 2. Delete the constraints file
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Remove `cibuildwheel/resources/constraints-pyodideXYZ.txt`.
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### 3. Update tests
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Remove references to the old identifier from the unit tests, integration tests, and drop any expected-wheel entries for it from the test helper.
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@@ -208,3 +208,9 @@ git push && git push --tags
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Then head to https://github.com/pypa/cibuildwheel/releases and create a GitHub release from the new tag, pasting in the changelog entry. Once the release is created inside GitHub, a CI job will create the assets and upload them to PyPI.
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If there were any schema updates, run `pipx run ./bin/generate_schema.py --schemastore > partial-cibuildwheel.json` and contribute the changes to SchemaStore.
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### Platform-specific maintenance
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This section is a stub. Please open a PR to add guidance for any platform you would like to help maintain!
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- **Pyodide**: see [Maintaining Pyodide support](_internal/pyodide-maintenance.md) for instructions and maintainer-specific information on updating Pyodide-related code in cibuildwheel and updating to new Pyodide releases.
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@@ -361,6 +361,8 @@ values are:
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- `pyodide-prerelease`: Pyodide versions that haven't released yet, if one is
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available. Safe if you are shipping a site with an early build, not for
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general distribution.
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- `pyodide-eol`: Enable Pyodide versions that are no longer the current stable
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release (if still available).
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- `all`: Enable all of the above.
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!!! caution
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+1
-3
@@ -159,8 +159,6 @@ By default, `ARM64` is not enabled when running on non-`ARM64` runners. Use [`CI
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## Pyodide/WebAssembly {: #pyodide}
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Pyodide is offered as an experimental feature in cibuildwheel.
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### System requirements
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Pyodide builds require a Linux or macOS machine.
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@@ -173,7 +171,7 @@ You must target pyodide with `--platform pyodide` (or use `--only` on the identi
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It is also possible to target a specific Pyodide version by setting the [`pyodide-version`](options.md#pyodide-version) option to the desired version. Users are responsible for setting an appropriate Pyodide version according to the `pyodide-build` version. A list is available in Pyodide's [cross-build environments metadata file](https://github.com/pyodide/pyodide/blob/main/pyodide-cross-build-environments.json), which can be viewed more easily by installing `pyodide-build` from PyPI and using `pyodide xbuildenv search --all` to see a compatibility table.
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If there are pre-releases available for a newer Pyodide version, the `pyodide-prerelease` [`enable`](options.md#enable) can be used to include pre-release versions.
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If there are pre-releases available for a newer Pyodide version, the `pyodide-prerelease` [`enable`](options.md#enable) can be used to include pre-release versions. To build for older Pyodide versions that are no longer the current stable, use the `pyodide-eol` [`enable`](options.md#enable).
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### Running tests
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