What's New in Pylint 4.1¶

:Release:4.1 :Date: TBA

Summary -- Release highlights¶

Startup is about 25% faster thanks to lazy imports. The import checker caches its isort configuration, which makes pylint about 17% faster on ansible. Finding the files to lint with --recursive=y no longer walks ignored directories such as .venv or node_modules, which took seconds on large trees. The duplicate-code checker and symilar also received optimizations that result in considerable performance improvements and memory use reduction on larger codebases. For example, pandas analysis went from 20 min to 55 s and pylint does not get OOM-killed when analyzing cpython anymore.

Python 3.15 support progresses: the unpacking in comprehensions added by PEP 798 no longer raises false positives, and the standard library deprecations of Python 3.15 are followed.

For CI, there is a new built-in junit output format (--output-format=junit), the NO_COLOR and FORCE_COLOR environment variables are respected, and the files to lint can now be set with the files option in the configuration file.

New checks: looping-through-iterator, impossible-comparison, chained-comparison-all-equal and using-comprehension-unpacking-in-unsupported-version.

Running with --jobs no longer duplicates the messages of extensions or ignores extensions enabled in the configuration.

Plugin authors: the confidence parameter can no longer be None, except in is_message_enabled, and the MSG_STATE_* constants are deprecated in favor of the MessageDisableReason enum.

The required astroid version is now 4.3.2. See the astroid changelog for additional fixes, features, and performance improvements applicable to pylint.

What's new in Pylint 4.1.2?¶

Release date: TBA

No significant changes.

What's new in Pylint 4.1.2?¶

Release date: 2026-10-03

False Positives Fixed¶

Fixed a false positive unbalanced-tuple-unpacking when unpacking a tuple concatenation whose elements have several possible values.

Fixed by upgrading astroid to 4.3.3.

Closes #2621 (#2621)

Other Bug Fixes¶

Fixed a crash when calling __bases__ on a class.

Fixed by upgrading astroid to 4.3.3.

Closes #11491 (#11491)
Fix a crash (astroid-error) when the class of a called attribute cannot be fully inferred, for example when the attribute is used as a with statement target or inside a comprehension.

Closes #11492 (#11492)
Fix a crash when a name bound by a type statement (a TypeVar) is used in a with statement.

Closes #11510 (#11510)
Fixed a crash (TypeError) in the variables checker when checking a class whose metaclass name binding has no line number, for example a class defined with metaclass=__annotations__.

Closes #11511 (#11511)
Fix a crash in the using-final-decorator-in-unsupported-version check when import final is used.

Closes #11521 (#11521)
Fix a crash when a plugin passes confidence=None to add_message, as pylint-pytest does, for a message that is disabled. confidence=None is accepted again and means UNDEFINED, like in pylint 4.0. Passing it explicitly to add_message, add_ignored_message or Message now emits a DeprecationWarning: it will raise an error in pylint 5.0.

Closes #11530 (#11530)

What's new in Pylint 4.1.1?¶

Release date: 2026-09-29

Other Changes¶

Pylint 4.1.0 could not be uploaded to PyPI, because it required an unreleased version of dill on Python 3.15, and PyPI refuses such a dependency. 4.1.1 is the first 4.1 release available on PyPI, see the 4.1.0 changes below.

Refs #11495 (#11495)

What's new in Pylint 4.1.0?¶

Release date: 2026-09-29

Breaking Changes¶

The confidence parameter is no longer nullable on any APIs except for is_message_enabled (where confidence=None means "don't filter by confidence"). The default became interfaces.UNDEFINED (an immutable value); the behavior is unchanged unless you were passing an explicit None. This avoids a runtime check in multiple function to set the default value conditionally.

The constants.MSG_STATE_* integer were replaced by a MessageDisableReason enum. The old names remain as deprecated aliases pointing at the enum members. MessageDisableReason is an IntEnum so existing code comparing the return of _get_message_state_scope to the literal 0 / 1 / 2 keeps working.

Refs #11018 (#11018)

New Features¶

Add support for ignore-pattern-in-long-lines to allow ignoring specific parts of a line when checking line length.

Refs #3352 (#3352)
Support for the NO_COLOR and FORCE_COLOR environment variables has been added. When running pylint, the reporter that writes to stdout is switched between text and colorized according to the requested mode. The order is: NO_COLOR > FORCE_COLOR > --output-format=....

Closes #3995 (#3995)
The dict-init-mutate message now includes a suggested dictionary literal showing how to combine the initialization and subsequent mutations into a single statement.

Closes #7819 (#7819)
Add a built-in junit output format (--output-format=junit) that produces JUnit-compatible XML output for CI/CD integration with Jenkins, Azure DevOps, GitLab CI, and GitHub Actions.

Closes #9143 (#9143)
Trailing pragmas understood by other common tooling (# type: ignore, # pyright: ignore, # noqa, # pragma: no cover and # pragma: no branch) are no longer counted toward the line length, so a line is not flagged as line-too-long solely because of such a pragma. This mirrors the existing behaviour for Pylint's own # pylint: pragmas.

Closes #10172 (#10172)
pyreverse: add --no-signatures to show method names without parameter lists or return type annotations in class diagrams.

Closes #10772 (#10772)
Add support for --known-first-party similar to --known-third-party.

Refs #10803 (#10803)

New Checks¶

Added a new checker looping-through-iterator (W4801) to detect when an iterator from an outer scope is consumed in a nested loop, which can lead to the iterator being unexpectedly exhausted.

Refs #2996 (#2996)
Add new checks impossible-comparison and chained-comparison-all-equal. impossible-comparison flags boolean conditions whose chain of numeric comparisons is logically contradictory and can never be true (for example a > b and b > a). chained-comparison-all-equal flags boolean conditions whose operands form a cycle of weak inequalities (<= or >=) and can be simplified to a chain of equalities (for example a >= b and b >= a is equivalent to a == b).

Closes #5814 (#5814)
Add using-comprehension-unpacking-in-unsupported-version (W2607), emitted when the code uses the unpacking in comprehensions added by PEP 798 while py-version still includes a Python version that cannot compile it.

Refs #10982 (#10982)

False Positives Fixed¶

Fix a false positive for unnecessary-negation (C0117) when negating a comparison between dict views (dict.keys()/dict.items()), which like set/frozenset support only a partial (subset/superset) ordering, so not a.items() <= b.items() is not equivalent to a.items() > b.items().

Closes #3668 (#3668)
Fix false positives for attribute-defined-outside-init / W0201 where __init__ (etc.) uses a helper method to create attributes.

Closes #5214 (#5214)
Fix a false positive for consider-using-generator and use-a-generator with an asynchronous list comprehension. Turning it into a generator expression would create an asynchronous generator, which those functions cannot consume.

Closes #7271 (#7271)
Fixed a false positive assigning-non-slot when assigning to an inherited descriptor through an instance returned by a method annotated with the subclass. This regressed in pylint 3.0.0.

Fixed by upgrading astroid to 4.1.0.

Closes #8053 (#8053)
Fixed a false positive no-member when a classmethod annotated with typing.Self is overridden in a subclass and its result is used directly, as in Subclass.build().only_on_subclass(). The return type is now narrowed to the subclass rather than the base class. This regressed in pylint 3.0.0.

Fixed by upgrading astroid to 4.1.0.

Closes #9159 (#9159)
Avoid emitting deprecated-class for imports inside a recognized sys.version_info guard.

Closes #9533 (#9533)
Fix a false positive for inconsistent-return-statements when an instance method annotated with NoReturn (or Never) is called via the class rather than an instance (e.g. MyClass.raise_method(obj)). The unbound method form is now recognised as never returning, matching the existing behaviour for the bound-method form.

Closes #9692 (#9692)
Fix used-before-assignment false positive for names bound in only some arms of an if/elif/else chain.

Closes #9879 (#9879)
Fix a false positive for useless-parent-delegation when a method overrides a method of a C-level parent whose signature cannot be inspected, such as Exception.__init__. Because Exception.__init__ accepts *args, an override taking only self narrows the accepted arguments and is not useless. Overrides of object.__init__ are still reported.

Closes #9994 (#9994)
Fixed a false positive no-name-in-module when a module is imported with an alias that shadows its base module and a function named format is called on the alias.

Fixed by upgrading astroid to 4.3.1.

Closes #10193 (#10193)
Fixed a false positive unsubscriptable-object on instances of a generic class defining __class_getitem__.

Closes #10360 (#10360)
Fixed a false positive unexpected-keyword-argument when passing dtype to numpy.concatenate().

Fixed by upgrading astroid to 4.3.1.

Closes #10548 (#10548)
Fix a false positive for unexpected-keyword-arg for dataclasses using generic type aliases (PEP 695).

Closes #10703 (#10703)
Fix false positive unreachable when calling a function with @overload where one signature returns NoReturn.

Closes #10785 (#10785)
Fix a false positive for too-many-function-args for dataclasses using generic type aliases (PEP 695).

Closes #10788 (#10788)
Fix a false positive relative-beyond-top-level error when linting specific files in namespace packages in parallel mode by augmenting sys.path before loading plugins and expanding files consistently for parallel workers.

Closes #10794 (#10794)

Fix # pylint: enable inside a try block leaking into the except handler. For example in the following code, no-member is no longer incorrectly re-enabled in the except block:

class Basket:
    # pylint: disable=no-member
    def pick(self):
        try:
            # pylint: enable=no-member
            print(self.apple)  # no-member emitted here
        except KeyError:
            print(self.banana)  # no-member NOT emitted here (correct)

Requires astroid 4.2.

Refs #10933 (#10933)

Fix false positives for the Python 3.15 syntax added by PEP 798, unpacking in comprehensions:
- star-needs-assignment-target (E0114) was emitted for the unpacked element of a comprehension, e.g. [*sub for sub in lists].
- consider-using-dict-comprehension (R1717) was emitted for dict([*pairs for pairs in nested]), which flattens its argument and is therefore not equivalent to a key/value dict comprehension.
Refs #10982 (#10982)
Fix access-member-before-definition false positive for bare type annotations (self.x: Type) that don't assign a value.

Refs #11015 (#11015)
Fix a false positive for assignment-from-no-return when the called function's body ends in an unconditional raise, such as pathlib.Path.readlink() on platforms without symlink support.

Closes #11114 (#11114)
Fix a false positive for protected-access when a protected member is accessed through self.__class__, which is now treated like type(self).

Closes #11160 (#11160)
Treat typing.NoReturn and typing.Never the same as NoReturn / Never when deciding that a call never returns.

Closes #11271 (#11271)
Fix a false positive for unreachable / W0101 on the statement following an instantiation of _sitebuiltins.Quitter (the class of the exit and quit builtins). Only calling the instance terminates, not creating it.

Closes #11310 (#11310)
Fixed a false positive unbalanced-tuple-unpacking when unpacking the args of an exception.

Fixed by upgrading astroid to 4.3.2.

Closes #11312 (#11312)
Fixed a false positive for unnecessary-semicolon when an f-string ending in ; is continued onto the next line with a backslash on Python 3.12+.

Closes #11444 (#11444)

False Negatives Fixed¶

missing-param-doc and missing-type-doc no longer false-negative on NumPy-style parameters whose type line includes a default value, e.g. number : int, default 0. Any text after the colon on the type line is now accepted as the type, matching the NumPy style guide.

Closes #6211 (#6211)
The docparams extension now emits multiple-constructor-doc when constructor parameters are documented in both the class docstring and the constructor docstring, even when the constructor method is skipped by no-docstring-rgx.

Closes #6692 (#6692)
chained-comparison is now emitted for additional simplifiable patterns (e.g. a > 1 and a > 10) and its message now includes the suggested simplification.

Refs #7611 (#7611)
Fix a false negative for abstract-method where a concrete subclass inheriting from an abstract class (without redeclaring abc.ABC or ABCMeta) was treated as abstract and silently exempted from the check. A class is now only considered abstract when it opts in explicitly, via direct abc.ABC inheritance, metaclass=ABCMeta, an @abstractmethod defined on the class, or being a Protocol.

Closes #7950 (#7950)
no-value-for-parameter is now emitted when a call unpacks a dictionary literal with ** and that dictionary does not provide a required argument.

Closes #8785 (#8785)
attribute-defined-outside-init / W0201 now reports attributes assigned with setattr(self, "name", value) outside defining methods. It no longer reports attributes assigned normally when a defining method of the class or of a parent initializes them with setattr.

Closes #9798 (#9798)
superfluous-parens (C0325) no longer false-negatives on a single parenthesised literal after the in keyword, e.g. x in ("foo"). The parentheses around a single string or number literal are now reported as superfluous, while a tuple (x in ("foo",)) or a larger expression (x in ("foo" + bar)) is still left untouched.

Closes #9878 (#9878)
comparison-with-itself now detects repeated attribute chains such as object.attribute == object.attribute.

Closes #10713 (#10713)
not-an-iterable and not-a-mapping are now also emitted for the value unpacked by PEP 798 comprehension unpacking, e.g. [*number for number in numbers] or {**number for number in numbers}.

Refs #10982 (#10982)
Fix a false negative in unnecessary-negation (C0117): not (a is not b) and not (a not in b) are now flagged (they simplify to a is b and a in b), consistent with the existing handling of is / in.

Closes #11140 (#11140)
Emit arguments-differ when an overridden special method takes a different number of parameters. Only renamed parameters and removed variadics stay exempt, and the constructor family (__new__, __init__, __init_subclass__ and __post_init__) is still fully ignored.

Closes #11295 (#11295)
access-member-before-definition is now also emitted when __init__ calls a method that reads an instance attribute which __init__ only assigns after the call.

Closes #11338 (#11338)
Fix a false negative for unspecified-encoding and bad-open-mode when the mode of an open call is a parameter of the enclosing function that has a default value. The default is now used to check the call, as a literal mode would be. Calls with such a mode stopped being reported in pylint 4.0.8.

Refs #11415 (#11415)

Other Bug Fixes¶

# pylint: disable comments at the beginning of an else block (or on the line just above the else keyword) now suppress messages in that block instead of being ignored.

Fixed by upgrading astroid to 4.3.1.

Closes #872 (#872)
dangerous-default-value now detects mutable default values in typing.NamedTuple field definitions.

Closes #3716 (#3716)
Repeated --output-format options now write reports to every requested file instead of only the last one.

Closes #8147 (#8147)
Fixed a crash when defining a functional namedtuple with a field name that changes under NFKC normalization, like "µ" (MICRO SIGN).

Fixed by upgrading astroid to 4.3.1.

Closes #8746 (#8746)
Fix a crash in pyreverse when a requested class cannot be inferred.

Closes #9797 (#9797)
Fix enabling checks from extensions which are disabled by default if multiple jobs are used.

Closes #10037 (#10037)
Fixed an AstroidBuildingError crash when inheriting from a generic dataclass that rebinds __init__ in __init_subclass__.

Fixed by upgrading astroid to 4.3.1.

Closes #10519 (#10519)
wrong-import-position now exempts try, if, with, and match blocks from marking the import boundary. Fixed async def not being detected as an import boundary. Pragma on non-import lines now suppresses following imports until the next non-import.

Closes #10589 (#10589)
Fix duplicate messages for extension checks if multiple jobs are used.

Refs #10642 (#10642)
Fix an issue where discovery can miss a similarly named directory if a shorter named directory is processed first.

Closes #10969 (#10969)
Follow the standard library deprecations of Python 3.15.

Refs #10982 (#10982)
Fixed inflated message occurrence counts in the final Messages report when running pylint in parallel mode with --jobs greater than 1.

Closes #10996 (#10996)
Fix a crash in consider-using-dict-items when the for loop or comprehension target is an attribute or a subscript (e.g. for self.key in d) rather than a simple variable name.

Closes #11173 (#11173)
nan-comparison now also recognizes math.nan, numpy.nan, Decimal("nan") and any name or attribute that pylint can infer to a NaN constant, such as a module level constant defined as math.nan. Only numpy.NaN -- removed in numpy 2.0 -- and float("nan") were detected before. Infinities are still not reported, as comparing against them is meaningful.

Refs #11219 (#11219)
Fix a crash in the comparison checker when a NaN comparison operand is a call to a name that cannot be inferred, such as 1 == b('nan').

Closes #11224 (#11224)
Fix a crash in invalid-class-object / E0243 and assigning-non-slot / E0237 when __class__ is assigned outside a simple assignment (e.g. for obj.__class__ in classes:).

Closes #11267 (#11267)
Avoid a fatal astroid-error / F0002 in invalid-name / C0103, stop-iteration-return / R1708, assigning-non-slot / E0237 and redefined-slots-in-subclass / W0244 for classes with duplicate or inconsistent bases, which leave the class without an MRO to walk.

Refs #11272 (#11272)
collections.abc.Callable and collections.abc.Buffer no longer count towards too-many-ancestors. Every other abstract base class in collections.abc was already ignored, so a class deriving from Callable was charged for an ancestor while an otherwise identical class deriving from Iterable was not.

Refs #11358 (#11358)
Fix import-private-name depending on the order of the checked files: type annotations are now collected for each module instead of only for the first module checked that contains an import. This removes a false positive on imports used only as annotations and a false negative on private imports used at runtime.

Closes #11466 (#11466)

Other Changes¶

Clarify how to choose the Python interpreter and py-version when linting a project that supports multiple Python versions.

Closes #5038 (#5038)
You can now set the files option in configuration files and on the command line. Passing files without the --files flag is still supported. This allows to set files to files = my_source_directory and invoking pylint with only the pylint command similar to how other CLI tools allow to do so. The help message can always be invoked with pylint -h or pylint --help.

Closes #5701 (#5701)
Removed messages (such as print-statement or apply-builtin) now have their own page in the documentation, with a link to the change that removed them. They are also listed in the messages overview alongside renamed messages.

Closes #6670 (#6670)
Documentation for options defined by Run, such as --errors-only and --init-hook, is now generated alongside checker configuration options.

Closes #6938 (#6938)
Document that the wrong-import-order (C0411) classification of imports as third-party vs first-party depends on the current working directory and recommend known-first-party as the deterministic workaround.

Closes #8801 (#8801)
Clarify related no-else-* messages so they say that only the first elif after the reported branch should change. Expand the no-else-return documentation to explain later branches and when retaining an elif chain can better communicate an exhaustive decision.

Closes #9274 (#9274)
assignment-from-no-return now names the callable that does not return anything and, for functions listed in the new known-side-effects-only-functions option, hints at the equivalent function to use instead (e.g. reversed(...) for reverse()).

Closes #10383 (#10383)

Internal Changes¶

Add assertDoesNotAddMessages to CheckerTestCase to assert that specific messages are not emitted, while allowing other messages to be present. This complements assertNoMessages which asserts that no messages at all are emitted.

Refs #9598 (#9598)
The primer now pairs residual messages — first by (symbol, path, obj) and then by exact source location — and reports altered messages as a single changed entry with a compact diff, rather than as a separate removal + addition. The location-based pass also catches symbol renames at the same code position (e.g. used-before-assignment → possibly-used-before-assignment). When several messages are eligible, the one closest to the original line wins, so pairs never cross. New messages are classified into fixed false positives (useless-suppression), astroid-error fatal errors, and the rest. astroid-error messages are excluded from pairing (their text embeds a unique crash-report path) so persistent crashes keep raising the prominent warning. Truncated comments are now cut at a line break and keep their code fences and <details> blocks closed.

Refs #10914 (#10914)
The primer's project cache key is now derived from the commits pinned in packages_to_prime.json instead of the remote branch tips. main and PR primer runs now share the same project cache and lint files in the same on-disk order, removing spurious diffs from primer comments (message positions and astroid inference results depend on the order in which modules are linted).

Closes #11192 (#11192)

Performance Improvements¶

Lazily import isort, dill, multiprocessing/concurrent.futures, and tomlkit so they are only loaded when actually needed. This reduces startup time by ~25% (e.g. --version: 91 => 67 ms, --help: 176 => 133 ms, single-file lint: 272 => 226 ms).

Closes #2866 (#2866)
Sped up the duplicate-code checker. When run inside pylint the checker now reuses the already-parsed AST instead of re-parsing every file like it has to do when launched via symilar, and it uses a rolling hash window with caching across file pairs. Additionally, a quadratic blow-up in the hash-matching phase is avoided by switching algorithm at a threshold, which previously caused the checker to hang on files with many repeated lines.

Speedup scales with codebase size from 1.5x on small projects (~10k lines), to 20x on large ones (500k+ lines). Memory usage also drops 12-27%. Codebases that previously hung or were OOM-killed could now complete.

Refs #10881 (#10881)
Skip isort classification in the import checker when no import-ordering message is enabled, and cache the isort configuration so it is built once instead of once per import statement. Skipping the isort processing become a negligible improvement once the caching is applied. pylint became ~17% faster on ansible (~=4500 imports) even with isort enabled.

Refs #10886, #2866, #10637 (#10886)
Finding the files to lint with --recursive=y is faster. Directories matching ignore, ignore-patterns or ignore-paths (such as .venv, .git or node_modules) are no longer walked, and neither are the packages already found. In a checkout of pylint with its virtual environment, this step is about three times faster when .git, .tox and .venv are ignored, and about twenty times faster when a large ignored tree is present.

Directories and files are now also visited in sorted order, so the order in which files are linted no longer depends on the file system. The order of messages can change once for projects whose file system listed directories in another order.

Closes #11005 (#11005)