v4.0.0

• Pylint now supports Python 3.14.

• Pylint's inference engine (astroid) is now much more precise,
  understanding implicit booleanness and ternary expressions. (Thanks @zenlyj!)

Consider this example:

class Result:
    errors: dict | None = None

result = Result()
if result.errors:
    result.errors[field_key]
    # inference engine understands result.errors cannot be None
    # pylint no longer raises unsubscriptable-object

The required astroid version is now 4.0.0. See the astroid changelog for additional fixes, features, and performance improvements applicable to pylint.

• Handling of invalid-name at the module level was patchy. Now,
  module-level constants that are reassigned are treated as variables and checked
  against --variable-rgx rather than --const-rgx. Module-level lists,
  sets, and objects can pass against either regex.

Here, LIMIT is reassigned, so pylint only uses --variable-rgx:

LIMIT = 500  # [invalid-name]
if sometimes:
    LIMIT = 1  # [invalid-name]

If this is undesired, refactor using exclusive assignment so that it is
evident that this assignment happens only once:

if sometimes:
    LIMIT = 1
else:
    LIMIT = 500  # exclusive assignment: uses const regex, no warning

Lists, sets, and objects still pass against either const-rgx or variable-rgx
even if reassigned, but are no longer completely skipped:

MY_LIST = []
my_list = []
My_List = []  # [invalid-name]

Remember to adjust the regexes and allow lists to your liking.

Breaking Changes

• invalid-name now distinguishes module-level constants that are assigned only once
  from those that are reassigned and now applies --variable-rgx to the latter. Values
  other than literals (lists, sets, objects) can pass against either the constant or
  variable regexes (e.g. "LOGGER" or "logger" but not "LoGgEr").

  Remember that --good-names or --good-names-rgxs can be provided to explicitly
  allow good names.

  Closes #3585

• The unused pylintrc argument to PyLinter.__init__() is deprecated
  and will be removed.

  Refs #6052

• Commented out code blocks such as # bar() # TODO: remove dead code will no longer emit fixme.

  Refs #9255

• pyreverse Run was changed to no longer call sys.exit() in its __init__.
  You should now call Run(args).run() which will return the exit code instead.
  Having a class that always raised a SystemExit exception was considered a bug.

  Normal usage of pyreverse through the CLI will not be affected by this change.

  Refs #9689

• The suggestion-mode option was removed, as pylint now always emits user-friendly hints instead
  of false-positive error messages. You should remove it from your conf if it's defined.

  Refs #9962

• The async.py checker module has been renamed to async_checker.py since async is a Python keyword
  and cannot be imported directly. This allows for better testing and extensibility of the async checker functionality.

  Refs #10071

• The message-id of continue-in-finally was changed from E0116 to W0136. The warning is
  now emitted for every Python version since it will raise a syntax warning in Python 3.14.
  See PEP 765 - Disallow return/break/continue that exit a finally block.

  Refs #10480

• Removed support for nmp.NaN alias for numpy.NaN being recognized in ':ref:nan-comparison'. Use np or numpy instead.

  Refs #10583

• Version requirement for isort has been bumped to >=5.0.0.
  The internal compatibility for older isort versions exposed via pylint.utils.IsortDriver has
  been removed.

  Refs #10637

New Features

• comparison-of-constants now uses the unicode from the ast instead of reformatting from
  the node's values preventing some bad formatting due to utf-8 limitation. The message now uses
  " instead of ' to better work with what the python ast returns.

  Refs #8736

• Enhanced pyreverse to properly distinguish between UML relationship types (association, aggregation, composition) based on object ownership semantics. Type annotations without assignment are now treated as associations, parameter assignments as aggregations, and object instantiation as compositions.

  Closes #9045
  Closes #9267

• The fixme check can now search through docstrings as well as comments, by using
  check-fixme-in-docstring = true in the [tool.pylint.miscellaneous] section.

  Closes #9255

• The use-implicit-booleaness-not-x checks now distinguish between comparisons
  used in boolean contexts and those that are not, enabling them to provide more accurate refactoring suggestions.

  Closes #9353

• The verbose option now outputs the filenames of the files that have been checked.
  Previously, it only included the number of checked and skipped files.

  Closes #9357

• colorized reporter now colorizes messages/categories that have been configured as fail-on in red inverse.
  This makes it easier to quickly find the errors that are causing pylint CI job failures.

  Closes #9898

• Enhanced support for @Property decorator in pyreverse to correctly display return types of annotated properties when generating class diagrams.

  Closes #10057

• Add --max-depth option to pyreverse to control diagram complexity. A depth of 0 shows only top-level packages, 1 shows one level of subpackages, etc.
  This helps manage visualization of large codebases by limiting the depth of displayed packages and classes.

  Refs #10077

• Handle deferred evaluation of annotations in Python 3.14.

  Closes #10149

• Enhanced pyreverse to properly detect aggregations for comprehensions (list, dict, set, generator).

  Closes #10236

• pyreverse: add support for colorized output when using output format mmd (MermaidJS) and html.

  Closes #10242

• pypy 3.11 is now officially supported.

  Refs #10287

• Add support for Python 3.14.

  Refs #10467

• Add naming styles for ParamSpec and TypeVarTuple that align with the TypeVar style.

  Refs #10541

New Checks

• Add match-statements checker and the following message:
  bare-name-capture-pattern.
  This will emit an error message when a name capture pattern is used in a match statement which would make the remaining patterns unreachable.
  This code is a SyntaxError at runtime.

  Closes #7128

• Add new check async-context-manager-with-regular-with to detect async context managers used with regular with statements instead of async with.

  Refs #10408

• Add break-in-finally warning. Using break inside the finally clause
  will raise a syntax warning in Python 3.14.
  See PEP 765 - Disallow return/break/continue that exit a finally block <https://peps.python.org/pep-0765/>_.

  Refs #10480

• Add new checks for invalid uses of class patterns in :keyword:match.

  • :ref:invalid-match-args-definition is emitted if :py:data:object.__match_args__ isn't a tuple of strings.
  • :ref:too-many-positional-sub-patterns if there are more positional sub-patterns than specified in :py:data:object.__match_args__.
  • :ref:multiple-class-sub-patterns if there are multiple sub-patterns for the same attribute.

  Refs #10559

• Add additional checks for suboptimal uses of class patterns in :keyword:match.

  • :ref:match-class-bind-self is emitted if a name is bound to self instead of
    using an as pattern.
  • :ref:match-class-positional-attributes is emitted if a class pattern has positional
    attributes when keywords could be used.

  Refs #10587

• Add a consider-math-not-float message. float("nan") and float("inf") are slower
  than their counterpart math.inf and math.nan by a factor of 4 (notwithstanding
  the initial import of math) and they are also not well typed when using mypy.
  This check also catches typos in float calls as a side effect.

  The :ref:pylint.extensions.code_style need to be activated for this check to work.

  Refs #10621

False Positives Fixed

• Fix a false positive for used-before-assignment when a variable defined under
  an if and via a named expression (walrus operator) is used later when guarded
  under the same if test.

  Closes #10061

• Fix :ref:no-name-in-module for members of concurrent.futures with Python 3.14.

  Closes #10632

False Negatives Fixed

• Fix false negative for used-before-assignment when a TYPE_CHECKING import is used as a type annotation prior to erroneous usage.

  Refs #8893

• Match cases are now counted as edges in the McCabe graph and will increase the complexity accordingly.

  Refs #9667

• Check module-level constants with type annotations for invalid-name.
  Remember to adjust const-naming-style or const-rgx to your liking.

  Closes #9770

• Fix false negative where function-redefined (E0102) was not reported for functions with a leading underscore.

  Closes #9894

• We now raise a logging-too-few-args for format string with no
  interpolation arguments at all (i.e. for something like logging.debug("Awaiting process %s")
  or logging.debug("Awaiting process {pid}")). Previously we did not raise for such case.

  Closes #9999

• Fix false negative for used-before-assignment when a function is defined inside a TYPE_CHECKING guard block and used later.

  Closes #10028

• Fix a false negative for possibly-used-before-assignment when a variable is conditionally defined
  and later assigned to a type-annotated variable.

  Closes #10421

• Fix false negative for deprecated-module when a __import__ method is used instead of import sentence.

  Refs #10453

• Count match cases for too-many-branches check.

  Refs #10542

• Fix false-negative where :ref:unused-import was not reported for names referenced in a preceding global statement.

  Refs #10633

Other Bug Fixes

• When displaying unicode with surrogates (or other potential UnicodeEncodeError),
  pylint will now display a '?' character (using encode(encoding="utf-8", errors="replace"))
  instead of crashing. The functional tests classes are also updated to handle this case.

  Closes #8736

• Fixed unidiomatic-typecheck only checking left-hand side.

  Closes #10217

• Fix a crash caused by malformed format strings when using .format with keyword arguments.

  Closes #10282

• Fix false positive inconsistent-return-statements when using quit() or exit() functions.

  Closes #10508

• Fix a crash in :ref:nested-min-max when using builtins.min or builtins.max
  instead of min or max directly.

  Closes #10626

• Fixed a crash in :ref:unnecessary-dict-index-lookup when the index of an enumerated list
  was deleted inside a for loop.

  Closes #10627

Other Changes

• Remove support for launching pylint with Python 3.9.
  Code that supports Python 3.9 can still be linted with the --py-version=3.9 setting.

  Refs #10405

Internal Changes

• Modified test framework to allow for different test output for different Python versions.

  Refs #10382