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v4.0.9

What's new in Pylint 4.0.9?

Release date: 2026-09-23

Security Fixes

• Someone without access to the configuration or linted code, but with access to the cache directory (predictable PYLINT_HOME on a multi-user host) can no longer write a crafted pickle that will runs arbitrary code when pylint access its stat cache. The result cache is now stored as JSON instead of pickle, preventing code-execution. The workaround is upgrading or not pointing PYLINT_HOME to an untrusted, shared, or group-writable directory. The default value, ~/.cache/pylint, is writable only by the user running pylint. (CVE with the same information pending)

False Positives Fixed

• Fixed a false positive for no-self-use on a method that only uses self before a locally defined class (or other nested method), because the checker's could-be-a-function tracking state was not restored after visiting the nested method.

  Closes #3705

• Fix a false positive for :ref:not-callable when calling functions constructed with types.FunctionType or types.LambdaType.

  Closes #7500

• Fix a false positive for unnecessary-direct-lambda-call when a directly called lambda in a class body wraps a comprehension containing an assignment expression. PEP 572 makes that a SyntaxError without the lambda's scope, so following the message produced code that would not compile.

  Closes #9294

• Fix a false positive for :ref:unnecessary-ellipsis when an ellipsis is the sole body statement of a method defined on a Protocol.

  Closes #9319

• Fix a false positive for :ref:bad-exception-cause when the bases of the class being raised from cannot be inferred, such as an exception deriving from a C extension class. :ref:raising-non-exception and :ref:catching-non-exception already guard the same inherit_from_std_ex

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• 303703f Bump pylint to 4.0.9, update changelog (#11448)
• b342384 Fix block-scoped disable leaking into sibling elif/else blocks (#11429) (#11445)
• 58c87cf Store the results cache as JSON instead of pickle
• e3f4942 [Backport maintenance/4.0.x] Fix crash on failed attribute inference (#11443)
• faf47f9 [Backport maintenance/4.0.x] Fix false positive no-self-use when a method con...
• 20c7bb9 [Backport maintenance/4.0.x] Fix a crash in method-hidden for methods named a...
• 47e6757 [Backport maintenance/4.0.x] Fix bad-exception-cause false positive when the ...
• ae3ee53 [Backport maintenance/4.0.x] Fix not-callable false positive for types.Functi...
• 3e444be [Backport maintenance/4.0.x] Fix a crash in unnecessary-default-type-args for...
• 8f2dd4f [Backport maintenance/4.0.x] Fix declare-non-slot false positives for ClassVa...
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