🎰 Slotscheck¶
Adding __slots__
to a class in Python is a great way to improve performance.
But to work properly, all base classes need to implement it — without overlap!
It’s easy to get wrong, and what’s worse: there is nothing warning you that you messed up.
✨ Until now! ✨
slotscheck
helps you validate your slots are working properly.
You can even use it to enforce the use of slots across (parts of) your codebase.
See my blog post
for the origin story behind slotscheck
.
Quickstart¶
Usage is quick from the command line:
python -m slotscheck [FILES]...
# or
slotscheck -m [MODULES]...
For example:
$ slotscheck -m sanic
ERROR: 'sanic.app:Sanic' defines overlapping slots.
ERROR: 'sanic.response:HTTPResponse' has slots but superclass does not.
Oh no, found some problems!
Scanned 72 module(s), 111 class(es).
Now get to fixing —
and add slotscheck
to your CI pipeline or
pre-commit
to prevent mistakes from creeping in again!
See here and
here for examples.
Features¶
Detect broken slots inheritance
Detect overlapping slots
Detect duplicate slots
Pre-commit hook
(Optionally) enforce the use of slots
See the documentation for more details and configuration options.
Why not a flake8 plugin?¶
Flake8 plugins need to work without running the code. Many libraries use conditional imports, star imports, re-exports, and define slots with decorators or metaclasses. This all but requires running the code to determine the slots and class tree.
There’s an issue to discuss the matter.
Notes¶
slotscheck
will try to import all submodules of the given package. If there are scripts withoutif __name__ == "__main__":
blocks, they may be executed.Even in the case that slots are not inherited properly, there may still be an advantage to using them (i.e. attribute access speed and some memory savings). However, in most cases this is unintentional.
slotscheck
allows you to ignore specific cases.Because
slotscheck
imports your code in arbitrary order, it can—in rare cases—result in confusing and randomly-occurring import errors in third-party libraries. In such a case, it is recommended to omit modules such as your tests and mypy plugins from the slotscheck run. See here. Alternatively, you can usePYTHONHASHSEED=<any value>
to make the import order deterministic. A solution to this problem is being worked on in this issue.
Installation¶
It’s available on PyPI.
pip install slotscheck
Contents¶
Changelog¶
0.19.1 (2024-10-19)¶
Explicit Python 3.13 support, drop Python 3.8 support
Documentation improvements
0.19.0 (2024-03-25)¶
Improved support for implicit/native namespace packages (#228, #230)
0.18.0 (2024-03-21)¶
Improved robustness of importing of namespace packages and built-in modules (#227)
0.17.3 (2024-02-04)¶
Fix packaging metadata issue where README/CHANGELOG were installed to the wrong location.
0.17.2 (2024-02-04)¶
Remove Python upper version constraint in package metadata
0.17.1 (2023-11-03)¶
Fixed
Generic
false positive in Python 3.12+ (#201).Remove
pkgutil
deprecation warning on Python 3.12+.Official Python 3.12 support.
0.17.0 (2023-07-31)¶
Drop Python 3.7 support.
Remove
typing-extensions
andimportlib_metadata
dependencies.More robust checks to prevent
Protocol
false positives.
0.16.5 (2023-03-01)¶
Don’t flag
TypedDict
fromtyping_extensions
in Python versions wheretyping
hasTypedDict
itself.
0.16.4 (2023-01-13)¶
Remove
tomli
dependency on Python 3.11+
0.16.3 (2023-01-03)¶
Fix broken
Protocol
import due to absenttyping_extensions
on Python <3.10.
0.16.2 (2022-12-29)¶
Don’t flag
Protocol
classes as needing slots if strictrequire-subclass
option is enabled.
0.16.1 (2022-11-21)¶
Don’t flag
TypedDict
subclasses as missing slots (#120).
0.16.0 (2022-11-01)¶
Breaking changes
The “strict-imports” default value was mistakenly
False
in contrast to what is documented. The default value is nowTrue
, in line with documentation. If you were relying on this permissive import behavior, you will need to set this option in the CLI or settings file.Drop Python 3.6 support
Bugfixes
Disabling “strict-imports” now also gracefully handles failed imports of the root module given (#113).
Features
Add official Python 3.11 support
0.15.0 (2022-08-09)¶
Fix error when encountering metaclass with slots (#106)
Improved detection of immutable classes on Python 3.10+ (#92)
0.14.1 (2022-06-26)¶
Gracefully handle inspection failure due to unimportable parent package (#90).
0.14.0 (2022-02-27)¶
Improved robustness of importing implicitly namespaced and extension packages (#64)
0.13.0 (2022-02-26)¶
Improved robustness of determining whether a class is pure Python (#65)
0.12.1 (2022-02-12)¶
Add helpful link to ‘failed to find module’ message.
0.12.0 (2022-02-06)¶
Support
setup.cfg
as alternate settings file (#52).
0.11.0 (2022-02-05)¶
Explicitly prevent ambiguous imports (#51).
0.10.2 (2022-01-30)¶
Correctly handle case when
__slots__
is defined as a single string (#47).
0.10.1 (2022-01-30)¶
Small improvements to verbose error messages.
0.10.0 (2022-01-29)¶
Detect duplicate slots (#21).
Improvements to docs.
Clarify pre-commit usage (#45).
0.9.0 (2022-01-25)¶
Support specifying the location of settings file with
--settings
option.Improved verbose error messages.
0.8.0 (2022-01-21)¶
Extension modules are now traversed.
Small tweaks to documentation.
0.7.2 (2022-01-18)¶
Recommend running as
python -m slotscheck
when checking files. Update pre-commit hook to reflect this.
0.7.1 (2022-01-18)¶
Add Python 3.6 support
0.7.0 (2022-01-18)¶
Breaking changes
Strict imports are now the default
Include/exclude regex patterns now use partial patch (like mypy, isort do).
Adjustments
Clarifications in documentation
Pre-commit hook uses verbose mode by default
0.6.0 (2022-01-17)¶
Breaking changes
Arguments are now file paths. Use the
-m/--module
option to scan modules.
Features
Support use as pre-commit hook.
Multiple modules or files allowed as input.
Document the types of slot errors.
0.5.3 (2022-01-14)¶
Fix typo in readme.
0.5.2 (2022-01-14)¶
Fix crash when encountering overlapping slots from multiple classes.
0.5.1 (2022-01-14)¶
Relax
tomli
dependency pin.
0.5.0 (2022-01-14)¶
More descriptive output on overlapping slots (#26).
Simplify slot requirement flags.
allow configuration by
pyproject.toml
(#28).
0.4.0 (2022-01-12)¶
Recognize builtin exceptions as not having slots.
Split
--exclude-modules
andexclude-classes
.Add flags to specify inclusion as well as exclusion of modules/classes.
Allow disabling slot inheritance check.
Add
--require-slots
option.
0.3.1 (2022-01-10)¶
Catch
BaseException
in module import.
0.3.0 (2022-01-10)¶
Add
--strict-imports
flag (#24)Detect overlapping slots (#10)
100% test coverage (#15)
Add
--exclude
flag (#9)
0.2.1 (2022-01-04)¶
Improved error message if module cannot be found (#18)
0.2.0 (2022-01-03)¶
Enable running with
-m slotscheck
(#13)
0.1.2 (2022-01-03)¶
Skip
__main__.py
in module scan to prevent running unintented code
0.1.1 (2022-01-03)¶
Improve output report
0.1.0 (2021-12-30)¶
Improve documentation
0.0.1 (2021-12-29)¶
Initial release