What's New in Pylint 2.16#

Release

2.16

Date

2023-02-01

Summary -- Release highlights#

In 2.16.0 we added aggregation and composition understanding in pyreverse, and a way to clear the cache in between run in server mode (originally for the VS Code integration). Apart from the bug fixes there's also a lot of new checks, and new extensions that have been asked for for a long time that were implemented.

If you want to benefit from all the new checks load the following plugins:

pylint.extensions.dict_init_mutate,
pylint.extensions.dunder,
pylint.extensions.typing,
pylint.extensions.magic_value,

We still welcome any community effort to help review, integrate, and add good/bad examples to the doc for <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!

Last but not least @clavedeluna and @nickdrozd became triagers, welcome to the team !

What's new in Pylint 2.16.1?#

Release date: 2023-02-02

Other Bug Fixes#

  • Fix a crash happening for python interpreter < 3.9 following a failed typing update.

    Closes #8161 (#8161)

What's new in Pylint 2.16.0?#

Release date: 2023-02-01

Changes requiring user actions#

  • The accept-no-raise-doc option related to missing-raises-doc will now be correctly taken into account all the time.

    Pylint will no longer raise missing-raises-doc (W9006) when no exceptions are documented and accept-no-raise-doc is true (issue #7208). If you were expecting missing-raises-doc errors to be raised in that case, you will now have to add accept-no-raise-doc=no in your configuration to keep the same behavior.

    Closes #7208 (#7208)

New Features#

  • Added the no-header output format. If enabled with --output-format=no-header, it will not include the module name in the output.

    Closes #5362 (#5362)

  • Added configuration option clear-cache-post-run to support server-like usage. Use this flag if you expect the linted files to be altered between runs.

    Refs #5401 (#5401)

  • Add --allow-reexport-from-package option to configure the useless-import-alias check not to emit a warning if a name is reexported from a package.

    Closes #6006 (#6006)

  • Update pyreverse to differentiate between aggregations and compositions. pyreverse checks if it's an Instance or a Call of an object via method parameters (via type hints) to decide if it's a composition or an aggregation.

    Refs #6543 (#6543)

New Checks#

  • Adds a pointless-exception-statement check that emits a warning when an Exception is created and not assigned, raised or returned.

    Refs #3110 (#3110)

  • Add a shadowed-import message for aliased imports.

    Closes #4836 (#4836)

  • Add new check called unbalanced-dict-unpacking to check for unbalanced dict unpacking in assignment and for loops.

    Closes #5797 (#5797)

  • Add new checker positional-only-arguments-expected to check for cases when positional-only arguments have been passed as keyword arguments.

    Closes #6489 (#6489)

  • Added singledispatch-method which informs that @singledispatch should decorate functions and not class/instance methods. Added singledispatchmethod-function which informs that @singledispatchmethod should decorate class/instance methods and not functions.

    Closes #6917 (#6917)

  • Rename broad-except to broad-exception-caught and add new checker broad-exception-raised which will warn if general exceptions BaseException or Exception are raised.

    Closes #7494 (#7494)

  • Added nested-min-max which flags min(1, min(2, 3)) to simplify to min(1, 2, 3).

    Closes #7546 (#7546)

  • Extended use-dict-literal to also warn about call to dict() when passing keyword arguments.

    Closes #7690 (#7690)

  • Add named-expr-without-context check to emit a warning if a named expression is used outside a context like if, for, while, or a comprehension.

    Refs #7760 (#7760)

  • Add invalid-slice-step check to warn about a slice step value of 0 for common builtin sequences.

    Refs #7762 (#7762)

  • Add consider-refactoring-into-while-condition check to recommend refactoring when a while loop is defined with a constant condition with an immediate if statement to check for break condition as a first statement.

    Closes #8015 (#8015)

Extensions#

  • Add new extension checker dict-init-mutate that flags mutating a dictionary immediately after the dictionary was created.

    Closes #2876 (#2876)

  • Added bad-dunder-name extension check, which flags bad or misspelled dunder methods. You can use the good-dunder-names option to allow specific dunder names.

    Closes #3038 (#3038)

  • Added consider-using-augmented-assign check for CodeStyle extension which flags x = x + 1 to simplify to x += 1. This check is disabled by default. To use it, load the code style extension with load-plugins=pylint.extensions.code_style and add consider-using-augmented-assign in the enable option.

    Closes #3391 (#3391)

  • Add magic-number plugin checker for comparison with constants instead of named constants or enums. You can use it with --load-plugins=pylint.extensions.magic_value.

    Closes #7281 (#7281)

  • Add redundant-typehint-argument message for typing plugin for duplicate assign typehints. Enable the plugin to enable the message with: --load-plugins=pylint.extensions.typing.

    Closes #7636 (#7636)

False Positives Fixed#

  • Fix false positive for unused-variable and unused-import when a name is only used in a string literal type annotation.

    Closes #3299 (#3299)

  • Document a known false positive for useless-suppression when disabling line-too-long in a module with only comments and no code.

    Closes #3368 (#3368)

  • trailing-whitespaces is no longer reported within strings.

    Closes #3822 (#3822)

  • Fix false positive for global-variable-not-assigned when a global variable is re-assigned via an ImportFrom node.

    Closes #4809 (#4809)

  • Fix false positive for use-maxsplit-arg with custom split method.

    Closes #4857 (#4857)

  • Fix logging-fstring-interpolation false positive raised when logging and f-string with %s formatting.

    Closes #4984 (#4984)

  • Fix false-positive for used-before-assignment in pattern matching with a guard.

    Closes #5327 (#5327)

  • Fix use-sequence-for-iteration when unpacking a set with *.

    Closes #5788 (#5788)

  • Fix deprecated-method false positive when alias for method is similar to name of deprecated method.

    Closes #5886 (#5886)

  • Fix false positive assigning-non-slot when a class attribute is re-assigned.

    Closes #6001 (#6001)

  • Fix false positive for too-many-function-args when a function call is assigned to a class attribute inside the class where the function is defined.

    Closes #6592 (#6592)

  • Fixes false positive abstract-method on Protocol classes.

    Closes #7209 (#7209)

  • Pylint now understands the kw_only keyword argument for dataclass.

    Closes #7290, closes #6550, closes #5857 (#7290)

  • Fix false positive for undefined-loop-variable in for-else loops that use a function having a return type annotation of NoReturn or Never.

    Closes #7311 (#7311)

  • Fix used-before-assignment for functions/classes defined in type checking guard.

    Closes #7368 (#7368)

  • Fix false positive for unhashable-member when subclassing dict and using the subclass as a dictionary key.

    Closes #7501 (#7501)

  • Fix the message for unnecessary-dunder-call for __aiter__ and __aneext__. Also only emit the warning when py-version >= 3.10.

    Closes #7529 (#7529)

  • Fix used-before-assignment false positive when else branch calls sys.exit or similar terminating functions.

    Closes #7563 (#7563)

  • Fix a false positive for used-before-assignment for imports guarded by typing.TYPE_CHECKING later used in variable annotations.

    Closes #7609 (#7609)

  • Fix a false positive for simplify-boolean-expression when multiple values are inferred for a constant.

    Closes #7626 (#7626)

  • unnecessary-list-index-lookup will not be wrongly emitted if enumerate is called with start.

    Closes #7682 (#7682)

  • Don't warn about stop-iteration-return when using next() over itertools.cycle.

    Closes #7765 (#7765)

  • Fixes used-before-assignment false positive when the walrus operator is used in a ternary operator.

    Closes #7779 (#7779)

  • Fix missing-param-doc false positive when function parameter has an escaped underscore.

    Closes #7827 (#7827)

  • Fixes method-cache-max-size-none false positive for methods inheriting from Enum.

    Closes #7857 (#7857)

  • multiple-statements no longer triggers for function stubs using inlined ....

    Closes #7860 (#7860)

  • Fix a false positive for used-before-assignment when a name guarded by if TYPE_CHECKING: is used as a type annotation in a function body and later re-imported in the same scope.

    Closes #7882 (#7882)

  • Prevent used-before-assignment when imports guarded by if TYPE_CHECKING are guarded again when used.

    Closes #7979 (#7979)

  • Fixes false positive for try-except-raise with multiple exceptions in one except statement if exception are in different namespace.

    Closes #8051 (#8051)

  • Fix invalid-name errors for typing_extension.TypeVar.

    Refs #8089 (#8089)

  • Fix no-kwoa false positive for context managers.

    Closes #8100 (#8100)

  • Fix a false positive for redefined-variable-type when async methods are present.

    Closes #8120 (#8120)

False Negatives Fixed#

  • Code following a call to quit, exit, sys.exit or os._exit will be marked as unreachable.

    Refs #519 (#519)

  • Emit used-before-assignment when function arguments are redefined inside an inner function and accessed there before assignment.

    Closes #2374 (#2374)

  • Fix a false negative for unused-import when one module used an import in a type annotation that was also used in another module.

    Closes #4150 (#4150)

  • Flag superfluous-parens if parentheses are used during string concatenation.

    Closes #4792 (#4792)

  • Emit used-before-assignment when relying on names only defined under conditions always testing false.

    Closes #4913 (#4913)

  • consider-using-join can now be emitted for non-empty string separators.

    Closes #6639 (#6639)

  • Emit used-before-assignment for further imports guarded by TYPE_CHECKING

    Previously, this message was only emitted for imports guarded directly under TYPE_CHECKING, not guarded two if-branches deep, nor when TYPE_CHECKING was imported from typing under an alias.

    Closes #7539 (#7539)

  • Fix a false negative for unused-import when a constant inside typing.Annotated was treated as a reference to an import.

    Closes #7547 (#7547)

  • consider-using-any-or-all message will now be raised in cases when boolean is initialized, reassigned during loop, and immediately returned.

    Closes #7699 (#7699)

  • Extend invalid-slice-index to emit an warning for invalid slice indices used with string and byte sequences, and range objects.

    Refs #7762 (#7762)

  • Fixes unnecessary-list-index-lookup false negative when enumerate is called with iterable as a kwarg.

    Closes #7770 (#7770)

  • no-else-return or no-else-raise will be emitted if except block always returns or raises.

    Closes #7788 (#7788)

  • Fix dangerous-default-value false negative when * is used.

    Closes #7818 (#7818)

  • consider-using-with now triggers for pathlib.Path.open.

    Closes #7964 (#7964)

Other Bug Fixes#

  • Fix bug in detecting unused-variable when iterating on variable.

    Closes #3044 (#3044)

  • Fix bug in scanning of names inside arguments to typing.Literal. See https://peps.python.org/pep-0586/#literals-enums-and-forward-references for details.

    Refs #3299 (#3299)

  • Update disallowed-name check to flag module-level variables.

    Closes #3701 (#3701)

  • Pylint will no longer deadlock if a parallel job is killed but fail immediately instead.

    Closes #3899 (#3899)

  • Fix ignored files being linted when passed on stdin.

    Closes #4354 (#4354)

  • Fix no-member false negative when augmented assign is done manually, without +=.

    Closes #4562 (#4562)

  • Any assertion on a populated tuple will now receive a assert-on-tuple warning.

    Closes #4655 (#4655)

  • missing-return-doc, missing-raises-doc and missing-yields-doc now respect the no-docstring-rgx option.

    Closes #4743 (#4743)

  • Update reimported help message for clarity.

    Closes #4836 (#4836)

  • consider-iterating-dictionary will no longer be raised if bitwise operations are used.

    Closes #5478 (#5478)

  • Using custom braces in msg-template will now work properly.

    Closes #5636 (#5636)

  • Pylint will now filter duplicates given to it before linting. The output should be the same whether a file is given/discovered multiple times or not.

    Closes #6242, #4053 (#6242)

  • Remove __index__ dunder method call from unnecessary-dunder-call check.

    Closes #6795 (#6795)

  • Fixed handling of -- as separator between positional arguments and flags. This was not actually fixed in 2.14.5.

    Closes #7003, Refs #7096 (#7003)

  • Don't crash on OSError in config file discovery.

    Closes #7169 (#7169)

  • Messages sent to reporter are now copied so a reporter cannot modify the message sent to other reporters.

    Closes #7214 (#7214)

  • Fixed a case where custom plugins specified by command line could silently fail.

    Specifically, if a plugin relies on the init-hook option changing sys.path before it can be imported, this will now emit a bad-plugin-value message. Before this change, it would silently fail to register the plugin for use, but would load any configuration, which could have unintended effects.

    Fixes part of #7264. (#7264)

  • Update modified_iterating checker to fix a crash with for loops on empty list.

    Closes #7380 (#7380)

  • Update wording for arguments-differ and arguments-renamed to clarify overriding object.

    Closes #7390 (#7390)

  • disable-next is now correctly scoped to only the succeeding line.

    Closes #7401 (#7401)

  • Fixed a crash in the unhashable-member checker when using a lambda as a dict key.

    Closes #7453 (#7453)

  • Add mailcap to deprecated modules list.

    Closes #7457 (#7457)

  • Fix a crash in the modified-iterating-dict checker involving instance attributes.

    Closes #7461 (#7461)

  • invalid-class-object does not crash anymore when __class__ is assigned alongside another variable.

    Closes #7467 (#7467)

  • --help-msg now accepts a comma-separated list of message IDs again.

    Closes #7471 (#7471)

  • Allow specifying non-builtin exceptions in the overgeneral-exception option using an exception's qualified name.

    Closes #7495 (#7495)

  • Report no-self-argument rather than no-method-argument for methods with variadic arguments.

    Closes #7507 (#7507)

  • Fixed an issue where syntax-error couldn't be raised on files with invalid encodings.

    Closes #7522 (#7522)

  • Fix false positive for redefined-outer-name when aliasing typing e.g. as t and guarding imports under t.TYPE_CHECKING.

    Closes #7524 (#7524)

  • Fixed a crash of the modified_iterating checker when iterating on a set defined as a class attribute.

    Closes #7528 (#7528)

  • Use py-version to determine if a message should be emitted for messages defined with max-version or min-version.

    Closes #7569 (#7569)

  • Improve bad-thread-instantiation check to warn if target is not passed in as a keyword argument or as a second argument.

    Closes #7570 (#7570)

  • Fixes edge case of custom method named next raised an astroid error.

    Closes #7610 (#7610)

  • Fixed a multi-processing crash that prevents using any more than 1 thread on MacOS.

    The returned module objects and errors that were cached by the linter plugin loader cannot be reliably pickled. This means that dill would throw an error when attempting to serialise the linter object for multi-processing use.

    Closes #7635. (#7635)

  • Fix crash that happened when parsing files with unexpected encoding starting with 'utf' like utf13.

    Closes #7661 (#7661)

  • Fix a crash when a child class with an __init__ method inherits from a parent class with an __init__ class attribute.

    Closes #7742 (#7742)

  • Fix valid-metaclass-classmethod-first-arg default config value from "cls" to "mcs" which would cause both a false-positive and false-negative.

    Closes #7782 (#7782)

  • Fixes a crash in the unnecessary_list_index_lookup check when using enumerate with start and a class attribute.

    Closes #7821 (#7821)

  • Fixes a crash in stop-iteration-return when the next builtin is called without arguments.

    Closes #7828 (#7828)

  • When pylint exit due to bad arguments being provided the exit code will now be the expected 32.

    Refs #7931 (#7931)

  • Fixes a ModuleNotFound exception when running pylint on a Django project with the pylint_django plugin enabled.

    Closes #7938 (#7938)

  • Fixed a crash when inferring a value and using its qname on a slice that was being incorrectly called.

    Closes #8067 (#8067)

  • Use better regex to check for private attributes.

    Refs #8081 (#8081)

  • Fix issue with new typing Union syntax in runtime context for Python 3.10+.

    Closes #8119 (#8119)

Other Changes#

  • Pylint now provides basic support for Python 3.11.

    Closes #5920 (#5920)

  • Update message for abstract-method to include child class name.

    Closes #7124 (#7124)

  • Update Pyreverse's dot and plantuml printers to detect when class methods are abstract and show them with italic font. For the dot printer update the label to use html-like syntax.

    Closes #7346 (#7346)

  • The docparams extension now considers typing in Numpy style docstrings as "documentation" for the missing-param-doc message.

    Refs #7398 (#7398)

  • Relevant DeprecationWarnings are now raised with stacklevel=2, so they have the callsite attached in the message.

    Closes #7463 (#7463)

  • Add a minimal option to pylint-config and its toml generator.

    Closes #7485 (#7485)

  • Add method name to the error messages of no-method-argument and no-self-argument.

    Closes #7507 (#7507)

  • Prevent leaving the pip install cache in the Docker image.

    Refs #7544 (#7544)

  • Add a keyword-only compare_constants argument to safe_infer.

    Refs #7626 (#7626)

  • Add default_enabled option to optional message dict. Provides an option to disable a checker message by default. To use a disabled message, the user must enable it explicitly by adding the message to the enable option.

    Refs #7629 (#7629)

  • Sort --generated-rcfile output.

    Refs #7655 (#7655)

  • epylint is now deprecated and will be removed in pylint 3.0.0. All emacs and flymake related files were removed and their support will now happen in an external repository : https://github.com/emacsorphanage/pylint.

    Closes #7737 (#7737)

  • Adds test for existing preferred-modules configuration functionality.

    Refs #7957 (#7957)

Internal Changes#

  • Add and fix regression tests for plugin loading.

    This shores up the tests that cover the loading of custom plugins as affected by any changes made to the sys.path during execution of an init-hook. Given the existing contract of allowing plugins to be loaded by fiddling with the path in this way, this is now the last bit of work needed to close Github issue #7264.

    Closes #7264 (#7264)