Development Status
- 5 - Production/Stable
Intended Audience
- Developers
Operating System
- POSIX
- MacOS :: MacOS X
- Microsoft :: Windows
Programming Language
- Cython
- Python
- Python :: 3
- Python :: 3.9
- Python :: 3.10
- Python :: 3.11
- Python :: 3.12
- Python :: 3.13
- Python :: 3.14
- Python :: Implementation :: CPython
- Python :: Implementation :: PyPy
frozenlist
Introduction
frozenlist.FrozenList is a list-like structure which implements collections.abc.MutableSequence. The list is mutable until FrozenList.freeze is called, after which list modifications raise RuntimeError:
>>> from frozenlist import FrozenList
>>> fl = FrozenList([17, 42])
>>> fl.append('spam')
>>> fl.append('Vikings')
>>> fl
<FrozenList(frozen=False, [17, 42, 'spam', 'Vikings'])>
>>> fl.freeze()
>>> fl
<FrozenList(frozen=True, [17, 42, 'spam', 'Vikings'])>
>>> fl.frozen
True
>>> fl.append("Monty")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "frozenlist/_frozenlist.pyx", line 97, in frozenlist._frozenlist.FrozenList.append
self._check_frozen()
File "frozenlist/_frozenlist.pyx", line 19, in frozenlist._frozenlist.FrozenList._check_frozen
raise RuntimeError("Cannot modify frozen list.")
RuntimeError: Cannot modify frozen list.
FrozenList is also hashable, but only when frozen. Otherwise it also throws a RuntimeError:
>>> fl = FrozenList([17, 42, 'spam'])
>>> hash(fl)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "frozenlist/_frozenlist.pyx", line 111, in frozenlist._frozenlist.FrozenList.__hash__
raise RuntimeError("Cannot hash unfrozen list.")
RuntimeError: Cannot hash unfrozen list.
>>> fl.freeze()
>>> hash(fl)
3713081631934410656
>>> dictionary = {fl: 'Vikings'} # frozen fl can be a dict key
>>> dictionary
{<FrozenList(frozen=True, [1, 2])>: 'Vikings'}
Installation
$ pip install frozenlist
Documentation
Communication channels
We have a Matrix Space #aio-libs-space:matrix.org which is also accessible via Gitter.
License
frozenlist is offered under the Apache 2 license.
Source code
The project is hosted on GitHub
Please file an issue in the bug tracker if you have found a bug or have some suggestions to improve the library.
Changelog
v1.8.0
(2025-10-05)
Contributor-facing changes
The reusable-cibuildwheel.yml workflow has been refactored to be more generic and ci-cd.yml now holds all the configuration toggles – by @webknjaz.
Related issues and pull requests on GitHub: #668.
When building wheels, the source distribution is now passed directly to the cibuildwheel invocation – by @webknjaz.
Related issues and pull requests on GitHub: #669.
Builds and tests have been added to ci-cd.yml for arm64 Windows wheels – by @finnagin.
Related issues and pull requests on GitHub: #677.
Started building wheels for CPython 3.14 – by @kumaraditya303.
Removed --config-settings=pure-python=false from requirements/dev.txt. Developers on CPython still get accelerated builds by default. To explicitly build a pure Python wheel, use pip install -e . --config-settings=pure-python=true – by @bdraco.
Related issues and pull requests on GitHub: #687.
v1.7.0
(2025-06-09)
Features
Packaging updates and notes for downstreams
Fixed an issue where frozenlist binary wheels would be built with debugging symbols and line tracing enabled, which significantly impacted performance. Line tracing is now disabled by default and can only be enabled explicitly – by @bdraco.
This change ensures that production builds are optimized for performance. Developers who need line tracing for debugging purposes can still enable it by:
Setting the FROZENLIST_CYTHON_TRACING environment variable
Using the --config-setting=with-cython-tracing=true option with pip
Related issues and pull requests on GitHub: #660.
Enabled PIP_CONSTRAINT environment variable in the build configuration to ensure the pinned Cython version from requirements/cython.txt is used during wheel builds.
Related issues and pull requests on GitHub: #661.
v1.6.2
(2025-06-03)
No significant changes.
v1.6.1
(2025-06-02)
Bug fixes
Correctly use cimport for including PyBool_FromLong – by @lysnikolaou.
Related issues and pull requests on GitHub: #653.
Packaging updates and notes for downstreams
Exclude _frozenlist.cpp from bdists/wheels – by @musicinmybrain.
Related issues and pull requests on GitHub: #649.
Updated to use Cython 3.1 universally across the build path – by @lysnikolaou.
Related issues and pull requests on GitHub: #654.
v1.6.0
(2025-04-17)
Bug fixes
Stopped implicitly allowing the use of Cython pre-release versions when building the distribution package – by @ajsanchezsanz and @markgreene74.
Related commits on GitHub: 41591f2.
Features
Implemented support for the free-threaded build of CPython 3.13 – by @lysnikolaou.
Related issues and pull requests on GitHub: #618.
Started building armv7l wheels – by @bdraco.
Related issues and pull requests on GitHub: #642.
Packaging updates and notes for downstreams
Stopped implicitly allowing the use of Cython pre-release versions when building the distribution package – by @ajsanchezsanz and @markgreene74.
Related commits on GitHub: 41591f2.
Started building wheels for the free-threaded build of CPython 3.13 – by @lysnikolaou.
Related issues and pull requests on GitHub: #618.
The packaging metadata switched to including an SPDX license identifier introduced in PEP 639 – by @cdce8p.
Related issues and pull requests on GitHub: #639.
Contributor-facing changes
GitHub Actions CI/CD is now configured to manage caching pip-ecosystem dependencies using re-actors/cache-python-deps – an action by @webknjaz that takes into account ABI stability and the exact version of Python runtime.
Related issues and pull requests on GitHub: #633.
Organized dependencies into test and lint dependencies so that no unnecessary ones are installed during CI runs – by @lysnikolaou.
Related issues and pull requests on GitHub: #636.
1.5.0 (2024-10-22)
Bug fixes
An incorrect signature of the __class_getitem__ class method has been fixed, adding a missing class_item argument under Python 3.8 and older.
This change also improves the code coverage of this method that was previously missing – by @webknjaz.
Improved documentation
Packaging updates and notes for downstreams
1.4.1 (2023-12-15)
Packaging updates and notes for downstreams
Declared Python 3.12 and PyPy 3.8-3.10 supported officially in the distribution package metadata.
Related issues and pull requests on GitHub: #553.
Replaced the packaging is replaced from an old-fashioned setup.py to an in-tree PEP 517 build backend – by @webknjaz.
Whenever the end-users or downstream packagers need to build frozenlist from source (a Git checkout or an sdist), they may pass a config_settings flag pure-python. If this flag is not set, a C-extension will be built and included into the distribution.
Here is how this can be done with pip:
$ python3 -m pip install . --config-settings=pure-python=This will also work with -e | --editable.
The same can be achieved via pypa/build:
$ python3 -m build --config-setting=pure-python=Adding -w | --wheel can force pypa/build produce a wheel from source directly, as opposed to building an sdist and then building from it.
Related issues and pull requests on GitHub: #560.
Contributor-facing changes
It is now possible to request line tracing in Cython builds using the with-cython-tracing PEP 517 config setting – @webknjaz.
This can be used in CI and development environment to measure coverage on Cython modules, but is not normally useful to the end-users or downstream packagers.
Here’s a usage example:
$ python3 -Im pip install . --config-settings=with-cython-tracing=trueFor editable installs, this setting is on by default. Otherwise, it’s off unless requested explicitly.
The following produces C-files required for the Cython coverage plugin to map the measurements back to the PYX-files:
$ python -Im pip install -e .Alternatively, the FROZENLIST_CYTHON_TRACING=1 environment variable can be set to do the same as the PEP 517 config setting.
Related issues and pull requests on GitHub: #560.
Coverage collection has been implemented for the Cython modules – by @webknjaz.
It will also be reported to Codecov from any non-release CI jobs.
Related issues and pull requests on GitHub: #561.
A step-by-step Release Guide guide has been added, describing how to release frozenlist – by @webknjaz.
This is primarily targeting the maintainers.
Related issues and pull requests on GitHub: #563.
Detailed Contributing Guidelines on authoring the changelog fragments have been published in the documentation – by @webknjaz.
Related issues and pull requests on GitHub: #564.
1.4.0 (2023-07-12)
The published source distribution package became buildable under Python 3.12.
Bugfixes
Removed an unused typing.Tuple import #411
Deprecations and Removals
Dropped Python 3.7 support. #413
Misc
1.3.3 (2022-11-08)
Fixed CI runs when creating a new release, where new towncrier versions fail when the current version section is already present.
1.3.2 (2022-11-08)
Misc
Updated the CI runs to better check for test results and to avoid deprecated syntax. #327
1.3.1 (2022-08-02)
The published source distribution package became buildable under Python 3.11.
1.3.0 (2022-01-18)
Bugfixes
Do not install C sources with binary distributions. #250
Deprecations and Removals
Dropped Python 3.6 support #274
1.2.0 (2021-10-16)
Features
FrozenList now supports being used as a generic type as per PEP 585, e.g. frozen_int_list: FrozenList[int] (requires Python 3.9 or newer). #172
Added support for Python 3.10. #227
Started shipping platform-specific wheels with the musl tag targeting typical Alpine Linux runtimes. #227
Started shipping platform-specific arm64 wheels for Apple Silicon. #227
1.1.1 (2020-11-14)
Bugfixes
Provide x86 Windows wheels. #169
1.1.0 (2020-10-13)
Features
Add support for hashing of a frozen list. #136
Support Python 3.8 and 3.9.
Provide wheels for aarch64, i686, ppc64le, s390x architectures on Linux as well as x86_64.
1.0.0 (2019-11-09)
Deprecations and Removals
Dropped support for Python 3.5; only 3.6, 3.7 and 3.8 are supported going forward. #24