What's New in Pylint 2.4

Release:2.4
Date:TBA

Summary -- Release highlights

New checkers

  • Added unnecessary-comprehension that detects unnecessary comprehensions.

    This check is emitted when pylint finds list-, set- or dict-comprehensions, that are unnecessary and can be rewritten with the list-, set- or dict-constructors.

    Close #2905

  • Added a new check, invalid-overridden-method

    This check is emitted when we detect that a method is overridden as a property or a property is overridden as a method. This can indicate a bug in the application code that will trigger a runtime error.

    Close #2670

  • Added a new check, redeclared-assigned-name

    This check is emitted when pylint detects that a name was assigned one or multiple times in the same assignment, which indicate a potential bug.

    Close #2898

  • Added a new check, self-assigning-variable

    This check is emitted when we detect that a variable is assigned to itself, which might indicate a potential bug in the code application.

    For example, the following would raise this warning:

    def new_a(attr, attr2):
      a_inst = Aclass()
      a_inst.attr2 = attr2
      # should be: a_inst.attr = attr, but have a typo
      attr = attr
      return a_inst
    

    Close #2930

  • Added a new check property-with-parameters which detects when a property has more than a single argument.

    Close #3006

  • Added subprocess-run-check to handle subprocess.run without explicitly set check keyword.

    Close #2848

  • We added a new check message dict-iter-missing-items. This is emitted when trying to iterate through a dict in a for loop without calling its .items() method.

    Closes #2761

  • We added a new check message missing-parentheses-for-call-in-test. This is emitted in case a call to a function is made inside a test but it misses parentheses.

  • A new check class-variable-slots-conflict was added.

    This check is emitted when pylint finds a class variable that conflicts with a slot name, which would raise a ValueError at runtime.

    For example, the following would raise an error:

    class A:
        __slots__ = ('first', 'second')
        first = 1
    
  • A new check preferred-module was added.

    This check is emitted when pylint finds an imported module that has a preferred replacement listed in preferred-modules.

    For example, you can set the preferred modules as xml:defusedxml,json:ujson to make pylint suggest using defusedxml instead of xml and ujson rather than json.

  • A new extension broad_try_clause was added.

    This extension enforces a configurable maximum number of statements inside of a try clause. This facilitates enforcing PEP 8's guidelines about try / except statements and the amount of code in the try clause.

    You can enable this extension using --load-plugins=pylint.extensions.broad_try_clause and you can configure the amount of statements in a try statement using --max-try-statements.

Other Changes

  • len-as-condition now only fires when a len(x) call is made without an explicit comparison.

    The message and description accompanying this checker has been changed reflect this new behavior, by explicitly asking to either rely on the fact that empty sequence are false or to compare the length with a scalar.

    OK:

    if len(x) == 0:
      pass
    
    while not len(x) == 0:
      pass
    
    assert len(x) > 5, message
    

    KO:

    if not len(x):
      pass
    
    while len(x) and other_cond:
      pass
    
    assert len(x), message
    
  • A file is now read from stdin if the --from-stdin flag is used on the command line. In addition to the --from-stdin flag a (single) file name needs to be specified on the command line, which is needed for the report.

  • The checker for ungrouped imports is now more permissive.

The import can now be sorted alphabetically by import style. This makes pylint compatible with isort.

The following imports do not trigger an ungrouped-imports anymore

import unittest
import zipfile
from unittest import TestCase
from unittest.mock import MagicMock
  • The checker for missing return documentation is now more flexible.

The following does not trigger a missing-return-doc anymore

def my_func(self):
    """This is a docstring.

    Returns
    -------
    :obj:`list` of :obj:`str`
        List of strings
    """
    return ["hi", "bye"] #@
  • signature-mutators CLI and config option was added.

With this option, users can choose to ignore too-many-function-args, unexpected-keyword-arg, and no-value-for-parameter for functions decorated with decorators that change the signature of a decorated function.

For example a test may want to make use of hypothesis. Adding hypothesis.extra.numpy.arrays to signature_mutators would mean that no-value-for-parameter would not be raised for:

@given(img=arrays(dtype=np.float32, shape=(3, 3, 3, 3)))
def test_image(img):
    ...