Summary -- Release highlights

With 2.14 pylint only supports Python version 3.7.2 and above.

We introduced several new checks among which duplicate-value for sets, comparison-of-constants, and checks related to lambdas. We removed no-init and made no-self-use optional as they were too opinionated. We also added an option to generate a toml configuration: --generate-toml-config.

We migrated to argparse from optparse and refactored the configuration handling thanks to Daniël van Noord. On the user side it should change the output of the --help command, and some inconsistencies and bugs should disappear. The behavior between options set in a config file versus on the command line will be more consistent. For us, it will permit to maintain this part of the code easily in the future and anticipate optparse's removal in Python 3.12.

As a result of the refactor there are a lot of internal deprecations. If you're a library maintainer that depends on pylint, please verify that you're ready for pylint 3.0 by activating deprecation warnings.

We continued the integration of pylint-error and are now at 33%!. We still welcome any community effort to help review, integrate, and add good/bad examples <https://github.com/PyCQA/pylint/issues/5953>`_. This should be doable without any pylint or astroid knowledge, so this is the perfect entrypoint if you want to contribute to pylint or open source without any experience with our code!

New checkers

  • Added new checker comparison-of-constants.

    Closes #6076

  • Added new checker typevar-name-mismatch: TypeVar must be assigned to a variable with the same name as its name argument.

    Closes #5224

  • invalid-enum-extension: Used when a class tries to extend an inherited Enum class.

    Closes #5501

  • Added new checker typevar-double-variance: The "covariant" and "contravariant" keyword arguments cannot both be set to "True" in a TypeVar.

    Closes #5895

  • Add new check unnecessary-dunder-call for unnecessary dunder method calls.

    Closes #5936

  • unnecessary-lambda-assignment: Lambda expression assigned to a variable. Define a function using the "def" keyword instead. unnecessary-direct-lambda-call: Lambda expression called directly. Execute the expression inline instead.

    Closes #5976

  • potential-index-error: Emitted when the index of a list or tuple exceeds its length. This checker is currently quite conservative to avoid false positives. We welcome suggestions for improvements.

    Closes #578

  • Added new checker unnecessary-list-index-lookup for indexing into a list while iterating over enumerate().

    Closes #4525

  • Added new message called duplicate-value which identifies duplicate values inside sets.

    Closes #5880

  • Added the super-without-brackets checker, raised when a super call is missing its brackets.

    Closes #4008

Removed checkers

  • The no-init (W0232) warning has been removed. It's ok to not have an __init__ in a class.

    Closes #2409

  • Removed the assign-to-new-keyword message as there are no new keywords in the supported Python versions any longer.

    Closes #4683

  • Moved no-self-use check to optional extension. You now need to explicitly enable this check using load-plugins=pylint.extensions.no_self_use.

    Closes #5502

Extensions

  • RedefinedLoopNameChecker

    • Added optional extension redefined-loop-name to emit messages when a loop variable is redefined in the loop body.

    Closes #5072

  • DocStringStyleChecker

    • Re-enable checker bad-docstring-quotes for Python <= 3.7.

    Closes #6087

  • NoSelfUseChecker

    • Added no-self-use check, previously enabled by default.

    Closes #5502

Other Changes

  • Started ignoring underscore as a local variable for too-many-locals.

    Closes #6488

  • Pylint can now be installed with an extra-require called spelling (pip install pylint[spelling]). This will add pyenchant to pylint's dependencies. You will still need to install the requirements for pyenchant (the enchant library and any dictionaries) yourself. You will also need to set the spelling-dict option.

    Refs #6462

  • Improved wording of the message of deprecated-module

    Closes #6169

  • Pylint now requires Python 3.7.2 or newer to run.

    Closes #4301

  • We made a greater effort to reraise failures stemming from the astroid library as AstroidError, with the effect that pylint emits astroid-error rather than merely fatal. Regardless, please report any such issues you encounter!

  • We have improved our recognition of inline disable and enable comments. It is now possible to disable bad-option-value inline (as long as you disable it before the bad option value is raised, i.e. disable=bad-option-value,bad-message not disable=bad-message,bad-option-value ) as well as certain other previously unsupported messages.

    Closes #3312

  • The main checker name is now main instead of master. The configuration does not need to be updated as sections' name are optional.

    Closes #5467

  • Update invalid-slots-object message to show bad object rather than its inferred value.

    Closes #6101

  • Fixed a crash in the not-an-iterable checker involving multiple starred expressions inside a call.

    Closes #6372

  • Fixed a crash in the unused-private-member checker involving chained private attributes.

    Closes #6709

  • Disable spellchecking of mypy rule names in ignore directives.

    Closes #5929

  • implicit-str-concat will now be raised on calls like open("myfile.txt" "a+b") too.

    Closes #6441

  • Fix a failure to respect inline disables for fixme occurring on the last line of a module when pylint is launched with --enable=fixme.

  • Removed the broken generate-man option.

    Closes #5283 Closes #1887

  • Fixed failure to enable deprecated-module after a disable=all by making ImportsChecker solely responsible for emitting deprecated-module instead of sharing responsibility with StdlibChecker. (This could have led to double messages.)

  • Added the generate-toml-config option.

    Refs #5462

  • bad-option-value will be emitted whenever a configuration value or command line invocation includes an unknown message.

    Closes #4324

  • Added the unrecognized-option message. Raised if we encounter any unrecognized options.

    Closes #5259

  • Fix false negative for bad-string-format-type if the value to be formatted is passed in as a variable holding a constant.

  • The concept of checker priority has been removed.

  • The cache-max-size-none checker has been renamed to method-cache-max-size-none.

    Closes #5670

  • The method-cache-max-size-none checker will now also check functools.cache.

    Closes #5670

  • BaseChecker classes now require the linter argument to be passed.

  • The set_config_directly decorator has been removed.

  • Don't report useless-super-delegation for the __hash__ method in classes that also override the __eq__ method.

    Closes #3934

  • Fix falsely issuing useless-suppression on the wrong-import-position checker.

    Closes #5219

  • Fixed false positive no-member for Enums with self-defined members.

    Closes #5138

  • Fix false negative for no-member when attempting to assign an instance attribute to itself without any prior assignment.

    Closes #1555

  • Changed message type from redefined-outer-name to redefined-loop-name (optional extension) for redefinitions of outer loop variables by inner loops.

    Closes #5608

  • By default the similarity checker will now ignore imports and ignore function signatures when computing duplication. If you want to keep the previous behaviour set ignore-imports and ignore-signatures to False.

  • Pylint now expands the user path (i.e. ~ to home/yusef/) and expands environment variables (i.e. home/$USER/$project to home/yusef/pylint for USER=yusef and project=pylint) for pyreverse's output-directory, import-graph, ext-import-graph, int-import-graph options, and the spell checker's spelling-private-dict-file option.

    Refs #6493

  • Don't emit unsubscriptable-object for string annotations. Pylint doesn't check if class is only generic in type stubs only.

    Closes #4369 and #6523

  • Fix pyreverse crash RuntimeError: dictionary changed size during iteration

    Refs #6612

  • Fix syntax for return type annotations in MermaidJS diagrams produced with pyreverse.

    Closes #6467

  • Fix type annotations of class and instance attributes using the alternative union syntax in pyreverse diagrams.

  • Fix bug where it writes a plain text error message to stdout, invalidating output formats.

    Closes #6597

  • The refactoring checker now also raises 'consider-using-a-generator' messages for max(), min() and sum().

    Refs #6595

  • Update ranges for using-constant-test and missing-parentheses-for-call-in-test error messages.

  • Don't emit no-member inside type annotations with from __future__ import annotations.

    Closes #6594

  • Fix unexpected-special-method-signature false positive for __init_subclass__ methods with one or more arguments.

    Closes #6644

Deprecations

  • The ignore-mixin-members option has been deprecated. You should now use the new ignored-checks-for-mixins option.

    Closes #5205

  • interfaces.implements has been deprecated and will be removed in 3.0. Please use standard inheritance patterns instead of __implements__.

    Refs #2287

  • All Interface classes in pylint.interfaces have been deprecated. You can subclass the respective normal classes to get the same behaviour. The __implements__ functionality was based on a rejected PEP from 2001: https://peps.python.org/pep-0245/

    Closes #2287

  • MapReduceMixin has been deprecated. BaseChecker now implements get_map_data and reduce_map_data. If a checker actually needs to reduce data it should define get_map_data as returning something different than None and let its reduce_map_data handle a list of the types returned by get_map_data. An example can be seen by looking at pylint/checkers/similar.py.

  • The config attribute of BaseChecker has been deprecated. You can use checker.linter.config to access the global configuration object instead of a checker-specific object.

    Refs #5392

  • The level attribute of BaseChecker has been deprecated: everything is now displayed in --help, all the time.

    Refs #5392

  • The set_option method of BaseChecker has been deprecated. You can use checker.linter.set_option to set an option on the global configuration object instead of a checker-specific object.

    Refs #5392

  • The options_providers attribute of ArgumentsManager has been deprecated.

    Refs #5392

  • Fix saving of persistent data files in environments where the user's cache directory and the linted file are on a different drive.

    Closes #6394

  • The method-cache-max-size-none checker will now also check functools.cache.

  • The config attribute of PyLinter is now of the argparse.Namespace type instead of optparse.Values.

    Refs #5392

  • UnsupportedAction has been deprecated.

    Refs #5392

  • OptionsManagerMixIn has been deprecated.

    Refs #5392

  • OptionParser has been deprecated.

    Refs #5392

  • Option has been deprecated.

    Refs #5392

  • OptionsProviderMixIn has been deprecated.

    Refs #5392

  • ConfigurationMixIn has been deprecated.

  • The option_groups attribute of PyLinter has been deprecated.

    Refs #5392

  • get_global_config has been deprecated. You can now access all global options from checker.linter.config.

    Refs #5392

  • OptionsManagerMixIn has been replaced with ArgumentsManager. ArgumentsManager is considered private API and most methods that were public on OptionsManagerMixIn have now been deprecated and will be removed in a future release.

    Refs #5392

  • OptionsProviderMixIn has been replaced with ArgumentsProvider. ArgumentsProvider is considered private API and most methods that were public on OptionsProviderMixIn have now been deprecated and will be removed in a future release.

    Refs #5392

  • pylint.pyreverse.ASTWalker has been removed, as it was only used internally by a single child class.

    Refs #6712

  • pyreverse: Resolving and displaying implemented interfaces that are defined by the __implements__ attribute has been deprecated and will be removed in 3.0.

    Refs #6713

  • is_class_subscriptable_pep585_with_postponed_evaluation_enabled has been deprecated. Use is_postponed_evaluation_enabled(node) and is_node_in_type_annotation_context(node) instead.

    Refs #6536