Summary -- Release highlights

In 2.16.0 we added aggregation and composition understanding in pyreverse, and a way to clear
the cache in between run in server mode (originally for the VS Code integration). Apart from the bug
fixes there's also a lot of new checks, and new extensions that have been asked for for a long time
that were implemented.

If you want to benefit from all the new checks load the following plugins::

pylint.extensions.dict_init_mutate,
pylint.extensions.dunder,
pylint.extensions.typing,
pylint.extensions.magic_value,

We still welcome any community effort to help review, integrate, and add good/bad examples to the doc for
#5953. This should be doable without any pylint or astroid
knowledge, so this is the perfect entrypoint if you want to contribute to pylint or open source without
any experience with our code!

Last but not least @clavedeluna and @nickdrozd became triagers, welcome to the team !

What's new in Pylint 2.16.0?

Changes requiring user actions

The accept-no-raise-doc option related to missing-raises-doc will now
be correctly taken into account all the time.

Pylint will no longer raise missing-raises-doc (W9006) when no exceptions are
documented and accept-no-raise-doc is true (issue #7208).
If you were expecting missing-raises-doc errors to be raised in that case,
you
will now have to add accept-no-raise-doc=no in your configuration to keep
the same behavior.
Closes #7208

New Features

Added the no-header output format. If enabled with
--output-format=no-header, it will not include the module name in the
output.
Closes #5362
Added configuration option clear-cache-post-run to support server-like
usage.
Use this flag if you expect the linted files to be altered between runs.
Refs #5401
Add --allow-reexport-from-package option to configure the
useless-import-alias check not to emit a warning if a name
is reexported from a package.
Closes #6006
Update pyreverse to differentiate between aggregations and compositions.
pyreverse checks if it's an Instance or a Call of an object via method
parameters (via type hints)
to decide if it's a composition or an aggregation.
Refs #6543

New Checks

Adds a pointless-exception-statement check that emits a warning when an
Exception is created and not assigned, raised or returned.
Refs #3110
Add a shadowed-import message for aliased imports.
Closes #4836
Add new check called unbalanced-dict-unpacking to check for unbalanced
dict unpacking
in assignment and for loops.
Closes #5797
Add new checker positional-only-arguments-expected to check for cases
when
positional-only arguments have been passed as keyword arguments.
Closes #6489
Added singledispatch-method which informs that @singledispatch should
decorate functions and not class/instance methods.
Added singledispatchmethod-function which informs that
@singledispatchmethod should decorate class/instance methods and not
functions.
Closes #6917
Rename broad-except to broad-exception-caught and add new checker
broad-exception-raised
which will warn if general exceptions BaseException or Exception are
raised.
Closes #7494
Added nested-min-max which flags min(1, min(2, 3)) to simplify to
min(1, 2, 3).
Closes #7546
Extended use-dict-literal to also warn about call to dict() when
passing keyword arguments.
Closes #7690
Add named-expr-without-context check to emit a warning if a named
expression is used outside a context like if, for, while, or
a comprehension.
Refs #7760
Add invalid-slice-step check to warn about a slice step value of 0
for common builtin sequences.
Refs #7762
Add consider-refactoring-into-while-condition check to recommend
refactoring when
a while loop is defined with a constant condition with an immediate if
statement to check for break condition as a first statement.
Closes #8015

Extensions

Add new extension checker dict-init-mutate that flags mutating a
dictionary immediately
after the dictionary was created.
Closes #2876
Added bad-dunder-name extension check, which flags bad or misspelled
dunder methods.
You can use the good-dunder-names option to allow specific dunder names.
Closes #3038
Added consider-using-augmented-assign check for CodeStyle extension
which flags x = x + 1 to simplify to x += 1.
This check is disabled by default. To use it, load the code style extension
with load-plugins=pylint.extensions.code_style and add
consider-using-augmented-assign in the enable option.
Closes #3391
Add magic-number plugin checker for comparison with constants instead of
named constants or enums.
You can use it with --load-plugins=pylint.extensions.magic_value.
Closes #7281
Add redundant-typehint-argument message for typing plugin for duplicate
assign typehints.
Enable the plugin to enable the message with:
--load-plugins=pylint.extensions.typing.
Closes #7636

False Positives Fixed

Fix false positive for unused-variable and unused-import when a name
is only used in a string literal type annotation.
Closes #3299
Document a known false positive for useless-suppression when disabling
line-too-long in a module with only comments and no code.
Closes #3368
trailing-whitespaces is no longer reported within strings.
Closes #3822
Fix false positive for global-variable-not-assigned when a global
variable is re-assigned via an ImportFrom node.
Closes #4809
Fix false positive for use-maxsplit-arg with custom split method.
Closes #4857
Fix logging-fstring-interpolation false positive raised when logging and
f-string with %s formatting.
Closes #4984
Fix false-positive for used-before-assignment in pattern matching
with a guard.
Closes #5327
Fix use-sequence-for-iteration when unpacking a set with *.
Closes #5788
Fix deprecated-method false positive when alias for method is similar to
name of deprecated method.
Closes #5886
Fix false positive assigning-non-slot when a class attribute is
re-assigned.
Closes #6001
Fix false positive for too-many-function-args when a function call is
assigned to a class attribute inside the class where the function is defined.
Closes #6592
Fixes false positive abstract-method on Protocol classes.
Closes #7209
Pylint now understands the kw_only keyword argument for dataclass.
Closes #7290, closes #6550, closes #5857
Fix false positive for undefined-loop-variable in for-else loops that
use a function
having a return type annotation of NoReturn or Never.
Closes #7311
Fix used-before-assignment for functions/classes defined in type checking
guard.
Closes #7368
Fix false positive for unhashable-member when subclassing dict and
using the subclass as a dictionary key.
Closes #7501
Fix the message for unnecessary-dunder-call for __aiter__ and
__aneext__. Also
only emit the warning when py-version >= 3.10.
Closes #7529
Fix used-before-assignment false positive when else branch calls
sys.exit or similar terminating functions.
Closes #7563
Fix a false positive for used-before-assignment for imports guarded by
typing.TYPE_CHECKING later used in variable annotations.
Closes #7609
Fix a false positive for simplify-boolean-expression when multiple values
are inferred for a constant.
Closes #7626
unnecessary-list-index-lookup will not be wrongly emitted if
enumerate is called with start.
Closes #7682
Don't warn about stop-iteration-return when using next() over
itertools.cycle.
Closes #7765
Fixes used-before-assignment false positive when the walrus operator
is used in a ternary operator.
Closes #7779
Fix missing-param-doc false positive when function parameter has an
escaped underscore.
Closes #7827
Fixes method-cache-max-size-none false positive for methods inheriting
from Enum.
Closes #7857
multiple-statements no longer triggers for function stubs using inlined
....
Closes #7860
Fix a false positive for used-before-assignment when a name guarded by
if TYPE_CHECKING: is used as a type annotation in a function body and
later re-imported in the same scope.
Closes #7882
Prevent used-before-assignment when imports guarded by if TYPE_CHECKING
are guarded again when used.
Closes #7979
Fixes false positive for try-except-raise with multiple exceptions in one
except statement if exception are in different namespace.
Closes #8051
Fix invalid-name errors for typing_extension.TypeVar.
Refs #8089
Fix no-kwoa false positive for context managers.
Closes #8100
Fix a false positive for redefined-variable-type when async methods
are present.
Closes #8120

False Negatives Fixed

Code following a call to quit, exit, sys.exit or os._exit
will be marked as unreachable.
Refs #519
Emit used-before-assignment when function arguments are redefined inside
an inner function and accessed there before assignment.
Closes #2374
Fix a false negative for unused-import when one module used an import in
a type annotation that was also used in another module.
Closes #4150
Flag superfluous-parens if parentheses are used during string
concatenation.
Closes #4792
Emit used-before-assignment when relying on names only defined under
conditions always testing false.
Closes #4913
consider-using-join can now be emitted for non-empty string separators.
Closes #6639
Emit used-before-assignment for further imports guarded by
TYPE_CHECKING
Previously, this message was only emitted for imports guarded directly under
TYPE_CHECKING, not guarded two if-branches deep, nor when
TYPE_CHECKING
was imported from typing under an alias.
Closes #7539
Fix a false negative for unused-import when a constant inside
typing.Annotated was treated as a reference to an import.
Closes #7547
consider-using-any-or-all message will now be raised in cases when
boolean is initialized, reassigned during loop, and immediately returned.
Closes #7699
Extend invalid-slice-index to emit an warning for invalid slice indices
used with string and byte sequences, and range objects.
Refs #7762
Fixes unnecessary-list-index-lookup false negative when enumerate is
called with iterable as a kwarg.
Closes #7770
no-else-return or no-else-raise will be emitted if except block
always returns or raises.
Closes #7788
Fix dangerous-default-value false negative when * is used.
Closes #7818
consider-using-with now triggers for pathlib.Path.open.
Closes #7964

Other Bug Fixes

Fix bug in detecting unused-variable when iterating on variable.
Closes #3044
Fix bug in scanning of names inside arguments to typing.Literal.
See https://peps.python.org/pep-0586/#literals-enums-and-forward-references
for details.
Refs #3299
Update disallowed-name check to flag module-level variables.
Closes #3701
Pylint will no longer deadlock if a parallel job is killed but fail
immediately instead.
Closes #3899
Fix ignored files being linted when passed on stdin.
Closes #4354
Fix no-member false negative when augmented assign is done manually,
without +=.
Closes #4562
Any assertion on a populated tuple will now receive a assert-on-tuple
warning.
Closes #4655
missing-return-doc, missing-raises-doc and missing-yields-doc now
respect
the no-docstring-rgx option.
Closes #4743
Update reimported help message for clarity.
Closes #4836
consider-iterating-dictionary will no longer be raised if bitwise
operations are used.
Closes #5478
Using custom braces in msg-template will now work properly.
Closes #5636
Pylint will now filter duplicates given to it before linting. The output
should
be the same whether a file is given/discovered multiple times or not.
Closes #6242, #4053
Remove __index__ dunder method call from unnecessary-dunder-call
check.
Closes #6795
Fixed handling of -- as separator between positional arguments and flags.
This was not actually fixed in 2.14.5.
Closes #7003, Refs #7096
Don't crash on OSError in config file discovery.
Closes #7169
Messages sent to reporter are now copied so a reporter cannot modify the
message sent to other reporters.
Closes #7214
Fixed a case where custom plugins specified by command line could silently
fail.
Specifically, if a plugin relies on the init-hook option changing
sys.path before
it can be imported, this will now emit a bad-plugin-value message. Before
this
change, it would silently fail to register the plugin for use, but would load
any configuration, which could have unintended effects.
Fixes part of #7264.
Update modified_iterating checker to fix a crash with for loops on
empty list.
Closes #7380
Update wording for arguments-differ and arguments-renamed to clarify
overriding object.
Closes #7390
disable-next is now correctly scoped to only the succeeding line.
Closes #7401
Fixed a crash in the unhashable-member checker when using a lambda as
a dict key.
Closes #7453
Add mailcap to deprecated modules list.
Closes #7457
Fix a crash in the modified-iterating-dict checker involving instance
attributes.
Closes #7461
invalid-class-object does not crash anymore when __class__ is
assigned alongside another variable.
Closes #7467
--help-msg now accepts a comma-separated list of message IDs again.
Closes #7471
Allow specifying non-builtin exceptions in the overgeneral-exception
option
using an exception's qualified name.
Closes #7495
Report no-self-argument rather than no-method-argument for methods
with variadic arguments.
Closes #7507
Fixed an issue where syntax-error couldn't be raised on files with
invalid encodings.
Closes #7522
Fix false positive for redefined-outer-name when aliasing typing
e.g. as t and guarding imports under t.TYPE_CHECKING.
Closes #7524
Fixed a crash of the modified_iterating checker when iterating on a set
defined as a class attribute.
Closes #7528
Use py-version to determine if a message should be emitted for messages
defined with max-version or min-version.
Closes #7569
Improve bad-thread-instantiation check to warn if target is not
passed in as a keyword argument
or as a second argument.
Closes #7570
Fixes edge case of custom method named next raised an astroid error.
Closes #7610
Fixed a multi-processing crash that prevents using any more than 1 thread on
MacOS.
The returned module objects and errors that were cached by the linter plugin
loader
cannot be reliably pickled. This means that dill would throw an error
when
attempting to serialise the linter object for multi-processing use.
Closes #7635.
Fix crash that happened when parsing files with unexpected encoding starting
with 'utf' like utf13.
Closes #7661
Fix a crash when a child class with an __init__ method inherits from a
parent class with an __init__ class attribute.
Closes #7742
Fix valid-metaclass-classmethod-first-arg default config value from "cls"
to "mcs"
which would cause both a false-positive and false-negative.
Closes #7782
Fixes a crash in the unnecessary_list_index_lookup check when using
enumerate with start and a class attribute.
Closes #7821
Fixes a crash in stop-iteration-return when the next builtin is
called without arguments.
Closes #7828
When pylint exit due to bad arguments being provided the exit code will now
be the expected 32.
Refs #7931
Fixes a ModuleNotFound exception when running pylint on a Django project
with the pylint_django plugin enabled.
Closes #7938
Fixed a crash when inferring a value and using its qname on a slice that was
being incorrectly called.
Closes #8067
Use better regex to check for private attributes.
Refs #8081
Fix issue with new typing Union syntax in runtime context for Python 3.10+.
Closes #8119

Other Changes

Pylint now provides basic support for Python 3.11.
Closes #5920
Update message for abstract-method to include child class name.
Closes #7124
Update Pyreverse's dot and plantuml printers to detect when class methods are
abstract and show them with italic font.
For the dot printer update the label to use html-like syntax.
Closes #7346
The docparams extension now considers typing in Numpy style docstrings
as "documentation" for the missing-param-doc message.
Refs #7398
Relevant DeprecationWarnings are now raised with stacklevel=2, so
they have the callsite attached in the message.
Closes #7463
Add a minimal option to pylint-config and its toml generator.
Closes #7485
Add method name to the error messages of no-method-argument and
no-self-argument.
Closes #7507
Prevent leaving the pip install cache in the Docker image.
Refs #7544
Add a keyword-only compare_constants argument to safe_infer.
Refs #7626
Add default_enabled option to optional message dict. Provides an option
to disable a checker message by default.
To use a disabled message, the user must enable it explicitly by adding the
message to the enable option.
Refs #7629
Sort --generated-rcfile output.
Refs #7655
epylint is now deprecated and will be removed in pylint 3.0.0. All emacs and
flymake related
files were removed and their support will now happen in an external
repository :
https://github.com/emacsorphanage/pylint.
Closes #7737
Adds test for existing preferred-modules configuration functionality.
Refs #7957

Internal Changes

Add and fix regression tests for plugin loading.
This shores up the tests that cover the loading of custom plugins as affected
by any changes made to the sys.path during execution of an init-hook.
Given the existing contract of allowing plugins to be loaded by fiddling with
the path in this way, this is now the last bit of work needed to close Github
issue #7264.
Closes #7264

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v2.16.0