# pyyaml-ft > YAML parser and emitter for Python with support for free-threading - **URL**: https://www.freshcrate.ai/projects/pyyaml-ft - **Author**: Lysandros Nikolaou - **Category**: Frameworks - **Latest version**: `8.0.0` (2026-04-21) - **License**: MIT - **Source**: https://github.com/Quansight-Labs/pyyaml-ft/issues - **Homepage**: https://github.com/Quansight-Labs/pyyaml-ft/ - **Language**: Python - **GitHub**: 1 stars, 1 forks - **Registry**: pypi (`pyyaml-ft`) - **Tags**: `pypi` ## Description PyYAML-ft ========= A full-featured YAML processing framework for Python with support for free-threading ## Why a fork? [PEP 703](https://peps.python.org/pep-0703/) introduced free-threaded Python as a separate build of CPython 3.13. Thread-safety issues that might have otherwise gone unnoticed are now much easier to trigger because of the absence of protection from the GIL. Also, because the free-threaded build is ABI-incompatible, extension modules need to be separate, free-threaded wheels and declare support for it. The PyYAML maintainers [decided to not port PyYAML to the free-threaded build](https://github.com/yaml/pyyaml/pull/830#issuecomment-2342475334) before the latter, along with Cython support for it, has been tested more extensively in real-world applications. Our rationale with this fork is to implement support for the free-threaded build, so that PyYAML can be tested with it by its users, even before the port is merged upstream. ### Differences compared with upstream - This fork uses Cython 3.1 which supports the free-threaded build, but whose support is still experimental. - `add_constructor`, `add_representer` and `add_*resolver` now all use thread-local registries, so you will have to explicitly register your custom constrcutors, representers and resolvers in each thread. Here's a small test showcasing that: ```python3 import io import threading import yaml_ft as yaml class Dice: def __init__(self, first, second): self.first = first self.second = second def __repr__(self): return f"Dice({self.first}, {self.second})" def construct_dice(constructor, node): mapping = constructor.construct_mapping(node) return Dice(**mapping) def load_dice(): yamlcode = io.StringIO("""\ - !dice first: 1 second: 6 - !dice first: 4 second: 4 """) print(f"Thread {threading.current_thread().name}") try: objs = yaml.load(yamlcode, Loader=yaml.CLoader) print(f"\t{objs=}") except Exception as e: print(f"\tException occurred: {e!s}") yaml.add_constructor("!dice", construct_dice, Loader=yaml.CLoader) load_dice() t = threading.Thread(target=load_dice) t.start() t.join() ``` Running the above script gives the following: ```bash ❯ python3.13t tmp/t.py Thread MainThread objs=[Dice(1, 6), Dice(4, 4)] Thread Thread-1 (load_dice) Exception occurred: could not determine a constructor for the tag '!dice' in "", line 1, column 3 ``` If you see new errors in multithreaded programs using `PyYAML-ft` that work with `PyYAML`, you may need to add calls to `yaml_ft.add_constructor`, `yaml_ft.add_representer` `yaml_ft.add_implicit_resolver` or `yaml_ft.add_path_resolver` in your thread worker function or worker initialization function. ### Python versions support Because PyYAML-ft is only aiming to exist for as long as upstream PyYAML does not support the free-threaded build, we recommend that users only conditionally switch to PyYAML-ft. At this time, PyYAML-ft **only supports Python 3.13 and 3.13t (i.e. the free-threaded build of 3.13)**. To switch to it, you can do the following in your `requirements.txt` file: ```requirements.txt ... PyYAML; python_version < '3.13' PyYAML-ft; python_version >= '3.13' ``` If you're developing a library that depends on PyYAML and you're using `pyproject.toml` to specify your dependencies, you can do the following: ```toml dependencies = [ ..., "PyYAML; python_version<'3.13'", "PyYAML-ft; python_version>='3.13'", ] ``` ### Different module name PyYAML-ft uses a different module name (namely `yaml_ft`) than upstream PyYAML on purpose, so that both can be installed in an environment at the same time. If your library depends on both for different Python versions, you can do the following for ease of use: ```python try: import yaml_ft as yaml except ModuleNotFoundError: import yaml ``` ## Installation To install, type `pip install PyYAML-ft`. When LibYAML bindings are installed (enabled by default), you may use the fast LibYAML-based parser and emitter as follows: >>> yaml.load(stream, Loader=yaml.CLoader) >>> yaml.dump(data, Dumper=yaml.CDumper) If you don't trust the input YAML stream, you should use: >>> yaml.safe_load(stream) ## Building from source and testing To build PyYAML-ft from source: 1. Clone [the fork repository](https://github.com/Quansight-Labs/pyyaml-ft) with `git clone https://github.com/Quansight-Labs/pyyaml-ft`. 1. Create a new virtual environment with `python3.13 -m venv .venv`. 1. Run `source .venv/bin/activate` to activate your new virtual environment. 1. Run `python3.13 -m pip install .`. This will build PyYAML-ft from source and install it in the newly created virtual environment. By default, the installation process will try to install the LibYAML bindings as well, but will fail silently if it canno ## Recent releases | Version | Date | Urgency | Changes | | --- | --- | --- | --- | | `8.0.0` | 2026-04-21 | Low | Imported from PyPI (8.0.0) | | `v8.0.0` | 2025-06-10 | Low | ## What's Changed * Rename yaml module to yaml_ft by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/20 - See more information on [the README](https://github.com/Quansight-Labs/pyyaml-ft#different-module-name). * Use pyyaml-ft when referencing the new repository by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/15 * Fix tests when the C extension isn't built by @ngoldbaum in https://github.com/Quansight-Labs/pyyaml-ft/pull/17 * Upgrade to Cython 3.1 final b | | `v8.0.0` | 2025-06-10 | Low | ## What's Changed * Rename yaml module to yaml_ft by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/20 - See more information on [the README](https://github.com/Quansight-Labs/pyyaml-ft#different-module-name). * Use pyyaml-ft when referencing the new repository by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/15 * Fix tests when the C extension isn't built by @ngoldbaum in https://github.com/Quansight-Labs/pyyaml-ft/pull/17 * Upgrade to Cython 3.1 final b | | `v8.0.0` | 2025-06-10 | Low | ## What's Changed * Rename yaml module to yaml_ft by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/20 - See more information on [the README](https://github.com/Quansight-Labs/pyyaml-ft#different-module-name). * Use pyyaml-ft when referencing the new repository by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/15 * Fix tests when the C extension isn't built by @ngoldbaum in https://github.com/Quansight-Labs/pyyaml-ft/pull/17 * Upgrade to Cython 3.1 final b | | `v8.0.0` | 2025-06-10 | Low | ## What's Changed * Rename yaml module to yaml_ft by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/20 - See more information on [the README](https://github.com/Quansight-Labs/pyyaml-ft#different-module-name). * Use pyyaml-ft when referencing the new repository by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/15 * Fix tests when the C extension isn't built by @ngoldbaum in https://github.com/Quansight-Labs/pyyaml-ft/pull/17 * Upgrade to Cython 3.1 final b | | `v8.0.0` | 2025-06-10 | Low | ## What's Changed * Rename yaml module to yaml_ft by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/20 - See more information on [the README](https://github.com/Quansight-Labs/pyyaml-ft#different-module-name). * Use pyyaml-ft when referencing the new repository by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/15 * Fix tests when the C extension isn't built by @ngoldbaum in https://github.com/Quansight-Labs/pyyaml-ft/pull/17 * Upgrade to Cython 3.1 final b | | `v8.0.0` | 2025-06-10 | Low | ## What's Changed * Rename yaml module to yaml_ft by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/20 - See more information on [the README](https://github.com/Quansight-Labs/pyyaml-ft#different-module-name). * Use pyyaml-ft when referencing the new repository by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/15 * Fix tests when the C extension isn't built by @ngoldbaum in https://github.com/Quansight-Labs/pyyaml-ft/pull/17 * Upgrade to Cython 3.1 final b | | `v8.0.0` | 2025-06-10 | Low | ## What's Changed * Rename yaml module to yaml_ft by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/20 - See more information on [the README](https://github.com/Quansight-Labs/pyyaml-ft#different-module-name). * Use pyyaml-ft when referencing the new repository by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/15 * Fix tests when the C extension isn't built by @ngoldbaum in https://github.com/Quansight-Labs/pyyaml-ft/pull/17 * Upgrade to Cython 3.1 final b | | `v8.0.0` | 2025-06-10 | Low | ## What's Changed * Rename yaml module to yaml_ft by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/20 - See more information on [the README](https://github.com/Quansight-Labs/pyyaml-ft#different-module-name). * Use pyyaml-ft when referencing the new repository by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/15 * Fix tests when the C extension isn't built by @ngoldbaum in https://github.com/Quansight-Labs/pyyaml-ft/pull/17 * Upgrade to Cython 3.1 final b | | `v8.0.0` | 2025-06-10 | Low | ## What's Changed * Rename yaml module to yaml_ft by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/20 - See more information on [the README](https://github.com/Quansight-Labs/pyyaml-ft#different-module-name). * Use pyyaml-ft when referencing the new repository by @lysnikolaou in https://github.com/Quansight-Labs/pyyaml-ft/pull/15 * Fix tests when the C extension isn't built by @ngoldbaum in https://github.com/Quansight-Labs/pyyaml-ft/pull/17 * Upgrade to Cython 3.1 final b | ## Citation - HTML: https://www.freshcrate.ai/projects/pyyaml-ft - Markdown: https://www.freshcrate.ai/projects/pyyaml-ft.md - Dependencies JSON: https://www.freshcrate.ai/api/projects/pyyaml-ft/deps _Generated by freshcrate.ai. 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