What's New in Pylint 3.0#

Release:

3.0.0

Date:

TBA

Summary -- Release highlights#

Note Bene for alpha users: Do not upgrade unless you want to test things out. Some changes will require a configuration change, that won't be compatible with 2.x. For example some extensions were removed in favor of a builtin message (compare-to-zero and compare-to-empty-string). We'll make a configuration upgrade tool available before 3.0.0 is out.

Pylint now provides some important usability and performance improvements, along with enacting necessary breaking changes and long-announced deprecations.

There's going to be frequent beta releases, before the official releases, everyone is welcome to try the betas so we find problems before the actual release.

The required astroid version is now 3.0.0. See the astroid changelog for additional fixes, features, and performance improvements applicable to pylint.

A new json2 reporter has been added. It features an enriched output that is easier to parse and provides more info, here's a sample output.

{
    "messages": [
        {
            "type": "convention",
            "symbol": "line-too-long",
            "message": "Line too long (1/2)",
            "messageId": "C0301",
            "confidence": "HIGH",
            "module": "0123",
            "obj": "",
            "line": 1,
            "column": 0,
            "endLine": 1,
            "endColumn": 4,
            "path": "0123",
            "absolutePath": "0123"
        }
    ],
    "statistics": {
        "messageTypeCount": {
            "fatal": 0,
            "error": 0,
            "warning": 0,
            "refactor": 0,
            "convention": 1,
            "info": 0
        },
        "modulesLinted": 1,
        "score": 5.0
    }
}

What's new in Pylint 3.0.0?#

Release date: TBA

Breaking Changes#

  • Enabling or disabling individual messages will now take effect even if an --enable=all or disable=all follows in the same configuration file (or on the command line).

    This means for the following example, fixme messages will now be emitted:

    pylint my_module --enable=fixme --disable=all

    To regain the prior behavior, remove the superfluous earlier option.

    Closes #3696 (#3696)

  • Remove support for launching pylint with Python 3.7. Code that supports Python 3.7 can still be linted with the --py-version=3.7 setting.

    Refs #6306 (#6306)

  • Disables placed in a try block now apply to the except block. Previously, they only happened to do so in the presence of an else clause.

    Refs #7767 (#7767)

  • pyreverse now uses a new default color palette that is more colorblind friendly. The color scheme is taken from Paul Tol's Notes. If you prefer other colors, you can use the --color-palette option to specify custom colors.

    Closes #8251 (#8251)

  • Everything related to the __implements__ construct was removed. It was based on PEP245 that was proposed in 2001 and rejected in 2006.

    The capability from pyreverse to take __implements__ into account when generating diagrams was also removed.

    Refs #8404 (#8404)

  • pyreverse: Support for the .vcg output format (Visualization of Compiler Graphs) has been dropped.

    Closes #8416 (#8416)

  • The warning when the now useless old pylint cache directory (pylint.d) was found was removed. The cache dir is documented in the FAQ.

    Refs #8462 (#8462)

  • Following a deprecation period, pylint.config.PYLINTRC was removed. Use the pylint.config.find_default_config_files generator instead.

    Closes #8862 (#8862)

Changes requiring user actions#

  • The invalid-name message no longer checks for a minimum length of 3 characters by default. (This was an unadvertised commingling of concerns between casing and name length, and users regularly reported this to be surprising.)

    If checking for a minimum length is still desired, it can be regained in two ways:

    • If you are content with a disallowed-name message (instead of invalid-name), then simply add the option bad-names-rgxs="^..?$", which will fail 1-2 character-long names. (Ensure you enable disallowed-name.)

    • If you would prefer an invalid-name message to be emitted, or would prefer finer-grained control over the circumstances in which messages are emitted (classes vs. methods, etc.), then avail yourself of the regex options described here. (In particular, take note of the commented out options in the "example configuration" given at the bottom of the section.) The prior regexes can be found in the pull request that removed the length requirements.

    Closes #2018 (#2018)

  • The compare to empty string checker (pylint.extensions.emptystring) and the compare to zero checker (pylint.extensions.compare-to-zero) have been removed and their checks are now part of the implicit booleaness checker:

    • compare-to-zero was renamed use-implicit-booleaness-not-comparison-to-zero and compare-to-empty-string was renamed use-implicit-booleaness-not-comparison-to-string and they now need to be enabled explicitly.

    • The pylint.extensions.emptystring and pylint.extensions.compare-to-zero extensions no longer exist and need to be removed from the load-plugins option.

    • Messages related to implicit booleaness were made more explicit and actionable. This permits to make their likeness explicit and will provide better performance as they share most of their conditions to be raised.

    Closes #6871 (#6871)

  • epylint was removed. It now lives at: https://github.com/emacsorphanage/pylint.

    Refs #7737 (#7737)

  • The overgeneral-exceptions option now only takes fully qualified names into account (builtins.Exception not Exception). If you overrode this option, you need to use the fully qualified name now.

    There's still a warning, but it will be removed in 3.1.0.

    Refs #8411 (#8411)

  • Following a deprecation period, it's no longer possible to use MASTER or master as configuration section in setup.cfg or tox.ini. It's bad practice to not start a section title with the tool name. Please use pylint.main instead.

    Refs #8465 (#8465)

  • Package stats are now printed when running Pyreverse and a --verbose flag was added to get the original output with parsed modules. You might need to activate the verbose option if you want to keep the old output.

    Closes #8973 (#8973)

New Features#

  • A new json2 reporter has been added. It features a more enriched output that is easier to parse and provides more info.

    Compared to json the only changes are that messages are now under the "messages" key and that "message-id" now follows the camelCase convention and is renamed to "messageId". The new reporter also reports the "score" of the modules you linted as defined by the evaluation option and provides statistics about the modules you linted.

    We encourage users to use the new reporter as the json reporter will no longer be maintained.

    Closes #4741 (#4741)

  • In Pyreverse package dependency diagrams, show when a module imports another only for type-checking.

    Closes #8112 (#8112)

  • Add new option (--show-stdlib, -L) to pyreverse. This is similar to the behavior of --show-builtin in that standard library modules are now not included by default, and this option will include them.

    Closes #8181 (#8181)

  • Add Pyreverse option to exclude standalone nodes from diagrams with --no-standalone.

    Closes #8476 (#8476)

New Checks#

  • Added DataclassChecker module and invalid-field-call checker to check for invalid dataclasses.field() usage.

    Refs #5159 (#5159)

  • Add return-in-finally to emit a message if a return statement was found in a finally clause.

    Closes #8260 (#8260)

  • Add a new checker kwarg-superseded-by-positional-arg to warn when a function is called with a keyword argument which shares a name with a positional-only parameter and the function contains a keyword variadic parameter dictionary. It may be surprising behaviour when the keyword argument is added to the keyword variadic parameter dictionary.

    Closes #8558 (#8558)

Extensions#

  • Add new prefer-typing-namedtuple message to the CodeStyleChecker to suggest rewriting calls to collections.namedtuple as classes inheriting from typing.NamedTuple on Python 3.6+.

    Requires load-plugins=pylint.extensions.code_style and enable=prefer-typing-namedtuple to be raised.

    Closes #8660 (#8660)

False Positives Fixed#

  • Extend concept of "function ambiguity" in safe_infer() from differing number of function arguments to differing set of argument names.

    Solves false positives in tensorflow.

    Closes #3613 (#3613)

  • Fix unused-argument false positive when __new__ does not use all the arguments of __init__.

    Closes #3670 (#3670)

  • Fix a false positive for invalid-name when a type-annotated class variable in an enum.Enum class has no assigned value.

    Refs #7402 (#7402)

  • Fix unused-import false positive for usage of six.with_metaclass.

    Closes #7506 (#7506)

  • Fix false negatives and false positives for too-many-try-statements, too-complex, and too-many-branches by correctly counting statements under a try.

    Refs #7767 (#7767)

  • When checking for unbalanced dict unpacking in for-loops, Pylint will now test whether the length of each value to be unpacked matches the number of unpacking targets. Previously, Pylint would test the number of values for the loop iteration, which would produce a false unbalanced-dict-unpacking warning.

    Closes #8156 (#8156)

  • Fix false positive for used-before-assignment when usage and assignment are guarded by the same test in different statements.

    Closes #8167 (#8167)

  • Adds asyncSetUp to the default defining-attr-methods list to silence attribute-defined-outside-init warning when using unittest.IsolatedAsyncioTestCase.

    Refs #8403 (#8403)

  • logging-not-lazy is not longer emitted for explicitly concatenated string arguments.

    Closes #8410 (#8410)

  • Fix false positive for isinstance-second-argument-not-valid-type when union types contains None.

    Closes #8424 (#8424)

  • invalid-name now allows for integers in typealias names: - now valid: Good2Name, GoodName2. - still invalid: _1BadName.

    Closes #8485 (#8485)

  • No longer consider Union as type annotation as type alias for naming checks.

    Closes #8487 (#8487)

  • unnecessary-lambda no longer warns on lambdas which use its parameters in their body (other than the final arguments), e.g. lambda foo: (bar if foo else baz)(foo).

    Closes #8496 (#8496)

  • Fixed unused-import so that it observes the dummy-variables-rgx option.

    Closes #8500 (#8500)

  • Union typed variables without assignment are no longer treated as TypeAlias.

    Closes #8540 (#8540)

  • Allow parenthesized implicitly concatenated strings when check-str-concat-over-line-jumps is enabled.

    Closes #8552. (#8552)

  • Fix false positive for positional-only-arguments-expected when a function contains both a positional-only parameter that has a default value, and **kwargs.

    Closes #8555 (#8555)

  • Fix false positive for keyword-arg-before-vararg when a positional-only parameter with a default value precedes *args.

    Closes #8570 (#8570)

  • Fix false positive for arguments-differ when overriding __init_subclass__.

    Closes #8919 (#8919)

  • Fix a false positive for no-value-for-parameter when a staticmethod is called in a class body.

    Closes #9036 (#9036)

False Negatives Fixed#

  • Emit used-before-assignment when calling module-level functions before definition.

    Closes #1144 (#1144)

  • Apply infer_kwarg_from_call() to more checks

    These mostly solve false negatives for various checks, save for one false positive for use-maxsplit-arg.

    Closes #7761 (#7761)

  • TypeAlias variables defined in functions are now checked for invalid-name errors.

    Closes #8536 (#8536)

  • Fix false negative for no-value-for-parameter when a function, whose signature contains both a positional-only parameter name and also *kwargs, is called with a keyword-argument for name.

    Closes #8559 (#8559)

  • Fix a false negative for too-many-arguments by considering positional-only and keyword-only parameters.

    Closes #8667 (#8667)

  • Emit assignment-from-no-return for calls to builtin methods like dict.update(). Calls to list.sort() now raise assignment-from-no-return rather than assignment-from-none for consistency.

    Closes #8714 Closes #8810 (#8714)

  • consider-using-augmented-assign is now applied to dicts and lists as well.

    Closes #8959. (#8959)

Other Bug Fixes#

  • Support duplicate-code message when parallelizing with --jobs.

    Closes #374 (#374)

  • Support cyclic-import message when parallelizing with --jobs.

    Closes #4171 (#4171)

  • --jobs can now be used with --load-plugins.

    This had regressed in astroid 2.5.0.

    Closes #4874 (#4874)

  • docparams extension considers type comments as type documentation.

    Closes #6287 (#6287)

  • When parsing comma-separated lists of regular expressions in the config, ignore commas that are inside braces since those indicate quantifiers, not delineation between expressions.

    Closes #7229 (#7229)

  • The ignored-modules option will now be correctly taken into account for no-name-in-module.

    Closes #7578 (#7578)

  • sys.argv is now always correctly considered as impossible to infer (instead of using the actual values given to pylint).

    Closes #7710 (#7710)

  • Avoid duplicative warnings for unqualified exception names in the overgeneral-exceptions setting when running with --jobs.

    Closes #7774 (#7774)

  • Don't show class fields more than once in Pyreverse diagrams.

    Closes #8189 (#8189)

  • Fix used-before-assignment false negative when TYPE_CHECKING imports are used in multiple scopes.

    Closes #8198 (#8198)

  • --clear-cache-post-run now also clears LRU caches for pylint utilities holding references to AST nodes.

    Closes #8361 (#8361)

  • Fix a crash when TYPE_CHECKING is used without importing it.

    Closes #8434 (#8434)

  • Fix a used-before-assignment false positive when imports are made under the TYPE_CHECKING else if branch.

    Closes #8437 (#8437)

  • Fix a regression of preferred-modules where a partial match was used instead of the required full match.

    Closes #8453 (#8453)

  • Fix a crash in pyreverse when "/" characters are used in the output filename e.g pyreverse -o png -p name/ path/to/project.

    Closes #8504 (#8504)

  • Don't show arrows more than once in Pyreverse diagrams.

    Closes #8522 (#8522)

  • Improve output of consider-using-generator message for min() calls with default keyword.

    Closes #8563 (#8563)

  • Fixed a crash when generating a configuration file: tomlkit.exceptions.TOMLKitError: Can't add a table to a dotted key caused by tomlkit v0.11.8.

    Closes #8632 (#8632)

  • Fix a line break error in Pyreverse dot output.

    Closes #8671 (#8671)

  • Fix a false positive for method-hidden when using cached_property decorator.

    Closes #8753 (#8753)

  • Dunder methods defined in lambda do not trigger unnecessary-dunder-call anymore, if they cannot be replaced by the non-dunder call.

    Closes #8769 (#8769)

  • Don't show duplicate type annotations in Pyreverse diagrams.

    Closes #8888 (#8888)

  • Fixing inconsistent hashing issue in BaseChecker causing some reports not being exported.

    Closes #9001 (#9001)

  • Don't add Optional to | annotations with None in Pyreverse diagrams.

    Closes #9014 (#9014)

  • Pyreverse doesn't show multiple class association arrows anymore, but only the strongest one.

    Refs #9045 (#9045)

  • Prevented data loss in the linter stats for messages relating to the linter itself (e.g. unknown-option-value), fixing problems with score, fail-on, etc.

    Closes #9059 (#9059)

  • Fix crash in refactoring checker when unary operand used with variable in for loop.

    Closes #9074 (#9074)

Other Changes#

  • Pylint now exposes its type annotations.

    Closes #5488 and #2079 (#5488)

  • Search for pyproject.toml recursively in parent directories up to a project or file system root.

    Refs #7163, Closes #3289 (#7163)

  • All code related to the optparse config parsing has been removed.

    Refs #8405 (#8405)

  • Pylint now supports python 3.12.

    Refs #8718 (#8718)

  • Add a CITATION.cff file to the root of the repository containing the necessary metadata to cite Pylint.

    Closes #8760 (#8760)

  • Renamed the "unneeded-not" error into "unnecessary_negation" to be clearer.

    Closes #8789 (#8789)

Internal Changes#

  • get_message_definition was removed from the base checker API. You can access message definitions through the MessageStore.

    Refs #8401 (#8401)

  • Everything related to the __implements__ construct was removed. It was based on PEP245 that was proposed in 2001 and rejected in 2006.

    All the classes inheriting Interface in pylint.interfaces were removed. Checker should only inherit BaseChecker or any of the other checker types from pylint.checkers. Reporter should only inherit BaseReporter.

    Refs #8404 (#8404)

  • modname and msg_store are now required to be given in FileState. collect_block_lines has also been removed. Pylinter.current_name cannot be null anymore.

    Refs #8407 (#8407)

  • Reporter.set_output was removed in favor of reporter.out = stream.

    Refs #8408 (#8408)

  • A number of old utility functions and classes have been removed:

    MapReduceMixin: To make a checker reduce map data simply implement get_map_data and reduce_map_data.

    is_inside_lambda: Use utils.get_node_first_ancestor_of_type(x, nodes.Lambda)

    check_messages: Use utils.only_required_for_messages

    is_class_subscriptable_pep585_with_postponed_evaluation_enabled: Use is_postponed_evaluation_enabled(node) and is_node_in_type_annotation_context(node)

    get_python_path: assumption that there's always an __init__.py is not true since python 3.3 and is causing problems, particularly with PEP 420. Use discover_package_path and pass source root(s).

    fix_import_path: Use augmented_sys_path and pass additional sys.path entries as an argument obtained from discover_package_path.

    get_global_option: Use checker.linter.config to get all global options.

    Related private objects have been removed as well.

    Refs #8409 (#8409)

  • colorize_ansi now only accepts a MessageStyle object.

    Refs #8412 (#8412)

  • Following a deprecation period, Pylinter.check now only works with sequences of strings, not strings.

    Refs #8463 (#8463)

  • Following a deprecation period, ColorizedTextReporter only accepts ColorMappingDict.

    Refs #8464 (#8464)

  • Following a deprecation period, MessageTest's end_line and end_col_offset must be accurate in functional tests (for python 3.8 or above on cpython, and for python 3.9 or superior on pypy).

    Refs #8466 (#8466)

  • Following a deprecation period, the do_exit argument of the Run class (and of the _Run class in testutils) were removed.

    Refs #8472 (#8472)

  • Following a deprecation period, the py_version argument of the MessageDefinition.may_be_emitted function is now required. The most likely solution is to use 'linter.config.py_version' if you need to keep using this function, or to use 'MessageDefinition.is_message_enabled' instead.

    Refs #8473 (#8473)

  • Following a deprecation period, the OutputLine class now requires the right number of argument all the time. The functional output can be regenerated automatically to achieve that easily.

    Refs #8474 (#8474)

  • Following a deprecation period, is_typing_guard, is_node_in_typing_guarded_import_block and is_node_in_guarded_import_block from pylint.utils were removed: use a combination of is_sys_guard and in_type_checking_block instead.

    Refs #8475 (#8475)

  • Following a deprecation period, the location argument of the Message class must now be a MessageLocationTuple.

    Refs #8477 (#8477)

  • Following a deprecation period, the check_single_file function of the Pylinter is replaced by Pylinter.check_single_file_item.

    Refs #8478 (#8478)

Performance Improvements#

  • pylint runs (at least) ~5% faster after improvements to astroid that make better use of the inference cache.

    Refs pylint-dev/astroid#529 (#529)

    • Optimize is_trailing_comma().

    • Cache class_is_abstract().

    Refs #1954 (#1954)

  • Exit immediately if all messages are disabled.

    Closes #8715 (#8715)