What's New in Pylint 2.9

Release

2.9

Date

2021-06-29

Summary -- Release highlights

Pylint is now compatible with python 3.10.

A lot of new checks have been added, some non-opinionated performance warnings like use-maxsplit-arg, some consensual style warnings like unnecessary-dict-index-lookup or new deprecation checks.

We're aiming to reduce pylint noise for first time users and making some new checks optional is a step in that direction. In order to do that we created an optional code style checker that can be loaded using pylint.extensions.code_style with the load-plugins options. More than ever, if as a veteran you want the most checks you can possibly get, you should check the list of pylint extensions..

New checkers

  • deprecated-decorator: Emitted when deprecated decorator is used.

  • consider-using-dict-items: Emitted when iterating over dictionary keys and then indexing the same dictionary with the key within loop body.

  • use-maxsplit-arg: Emitted either when accessing only the first or last element of str.split().

  • An ignore_signatures option has been added to the similarity checker. It will permits to reduce false positives when multiple functions have the same parameters.

  • unnecessary-dict-index-lookup: Emitted when iterating over dictionary items (key-value pairs) and accessing the value by index lookup.

  • consider-using-from-import: Emitted when a submodule/member of a package is imported and aliased with the same name.

  • New checker unused-private-member: Emitted when a private member (i.e., starts with __) of a class is defined but not used.

  • New checker invalid-class-object: Emitted when a non-class is assigned to a __class__ attribute.

  • invalid-all-format: Emitted when __all__ has an invalid format, i.e. isn't a tuple or list.

  • New checker await-outside-async: Emitted when await is used outside an async function.

  • Add new extension CodeStyleChecker. It includes checkers that can improve code consistency. As such they don't necessarily provide a performance benefit and are often times opinionated.

    • consider-using-tuple: Emitted when an in-place defined list or set can be replaced by a tuple.

    • consider-using-namedtuple-or-dataclass: Emitted when dictionary values can be replaced by namedtuples or dataclass instances.

Other Changes

  • Fix false-positive consider-using-with (R1732) if a ternary conditional is used together with with

  • Fix false-positive consider-using-with (R1732) if contextlib.ExitStack takes care of calling the __exit__ method

  • Add type annotations to pyreverse dot files

  • Pylint's tags are now the standard form vX.Y.Z and not pylint-X.Y.Z anymore.

  • Fix false-positive too-many-ancestors when inheriting from builtin classes, especially from the collections.abc module

  • The output messages for arguments-differ error message have been customized based on the different error cases.

  • New option --fail-on=<msg ids> to return non-zero exit codes regardless of fail-under value.

  • A new error called arguments-renamed has been created, which identifies any changes at the parameter names of overridden functions. It aims to separate the functionality of arguments-differ.

  • Fix incompatibility with Python 3.6.0 caused by typing.Counter and typing.NoReturn usage

  • Allow comma-separated list in output-format and separate output files for each specified format. Each output file can be defined after a semicolon for example : --output-format=json:myfile.json,colorized

  • The using-constant-test checker now detects constant tests consisting of list literals like [] and [1, 2, 3].

  • ignore-paths configuration directive has been added. Defined regex patterns are matched against file path.

  • Added handling of floating point values when parsing configuration from pyproject.toml

  • Fix false positive useless-type-doc on ignored argument using pylint.extensions.docparams when a function was typed using pep484 but not inside the docstring.

  • Fix missing support for detecting deprecated aliases to existing functions/methods. functions/methods.

  • Added various deprecated functions/methods for python 3.10, 3.7, 3.6 and 3.3

  • No longer emit consider-using-with for ThreadPoolExecutor and ProcessPoolExecutor as they have legitimate use cases without a with block.

  • Fix crash if a callable returning a context manager was assigned to a list or dict item