Optional Pylint checkers in the extensions module

Pylint provides the following optional plugins:

You can activate any or all of these extensions by adding a load-plugins line to the MASTER section of your .pylintrc, for example:

load-plugins=pylint.extensions.docparams,pylint.extensions.docstyle

Broad Try Clause checker

This checker is provided by pylint.extensions.broad_try_clause. Verbatim name of the checker is broad_try_clause.

Broad Try Clause checker Options

max-try-statements

Maximum number of statements allowed in a try clause

Default: 1

Broad Try Clause checker Messages

too-many-try-statements (W0717)

Try clause contains too many statements.

Code Style checker

This checker is provided by pylint.extensions.code_style. Verbatim name of the checker is code_style.

Code Style checker Documentation

Checkers that can improve code consistency. As such they don't necessarily provide a performance benefit and are often times opinionated.

Code Style checker Options

max-line-length-suggestions

Max line length for which to sill emit suggestions. Used to prevent optional suggestions which would get split by a code formatter (e.g., black). Will default to the setting for max-line-length.

Code Style checker Messages

consider-using-tuple (R6102)

Consider using an in-place tuple instead of list Only for style consistency! Emitted where an in-place defined list can be replaced by a tuple. Due to optimizations by CPython, there is no performance benefit from it.

consider-using-namedtuple-or-dataclass (R6101)

Consider using namedtuple or dataclass for dictionary values Emitted when dictionary values can be replaced by namedtuples or dataclass instances.

consider-using-assignment-expr (R6103)

Use '%s' instead Emitted when an if assignment is directly followed by an if statement and both can be combined by using an assignment expression :=. Requires Python 3.8 and py-version >= 3.8.

Compare-To-Empty-String checker

This checker is provided by pylint.extensions.emptystring. Verbatim name of the checker is compare-to-empty-string.

Compare-To-Empty-String checker Messages

compare-to-empty-string (C1901)

Avoid comparisons to empty string Used when Pylint detects comparison to an empty string constant.

Compare-To-Zero checker

This checker is provided by pylint.extensions.comparetozero. Verbatim name of the checker is compare-to-zero.

Compare-To-Zero checker Messages

compare-to-zero (C2001)

Avoid comparisons to zero Used when Pylint detects comparison to a 0 constant.

Confusing Elif checker

This checker is provided by pylint.extensions.confusing_elif. Verbatim name of the checker is confusing_elif.

Confusing Elif checker Messages

confusing-consecutive-elif (R5601)

Consecutive elif with differing indentation level, consider creating a function to separate the inner elif Used when an elif statement follows right after an indented block which itself ends with if or elif. It may not be ovious if the elif statement was willingly or mistakenly unindented. Extracting the indented if statement into a separate function might avoid confusion and prevent errors.

Consider Ternary Expression checker

This checker is provided by pylint.extensions.consider_ternary_expression. Verbatim name of the checker is consider_ternary_expression.

Consider Ternary Expression checker Messages

consider-ternary-expression (W0160)

Consider rewriting as a ternary expression Multiple assign statements spread across if/else blocks can be rewritten with a single assignment and ternary expression

Deprecated Builtins checker

This checker is provided by pylint.extensions.bad_builtin. Verbatim name of the checker is deprecated_builtins.

Deprecated Builtins checker Documentation

This used to be the bad-builtin core checker, but it was moved to an extension instead. It can be used for finding prohibited used builtins, such as map or filter, for which other alternatives exists.

If you want to control for what builtins the checker should warn about, you can use the bad-functions option:

$ pylint a.py --load-plugins=pylint.extensions.bad_builtin --bad-functions=apply,reduce
...

Deprecated Builtins checker Options

bad-functions

List of builtins function names that should not be used, separated by a comma

Default: map,filter

Deprecated Builtins checker Messages

bad-builtin (W0141)

Used builtin function %s Used when a disallowed builtin function is used (see the bad-function option). Usual disallowed functions are the ones like map, or filter , where Python offers now some cleaner alternative like list comprehension.

Design checker

This checker is provided by pylint.extensions.mccabe. Verbatim name of the checker is design.

Design checker Documentation

You can now use this plugin for finding complexity issues in your code base.

Activate it through pylint --load-plugins=pylint.extensions.mccabe. It introduces a new warning, too-complex, which is emitted when a code block has a complexity higher than a preestablished value, which can be controlled through the max-complexity option, such as in this example:

$ cat a.py
def f10():
    """McCabe rating: 11"""
    myint = 2
    if myint == 5:
        return myint
    elif myint == 6:
        return myint
    elif myint == 7:
        return myint
    elif myint == 8:
        return myint
    elif myint == 9:
        return myint
    elif myint == 10:
        if myint == 8:
            while True:
                return True
        elif myint == 8:
            with myint:
                return 8
    else:
        if myint == 2:
            return myint
        return myint
    return myint
$ pylint a.py --load-plugins=pylint.extensions.mccabe
R:1: 'f10' is too complex. The McCabe rating is 11 (too-complex)
$ pylint a.py --load-plugins=pylint.extensions.mccabe --max-complexity=50
$

Design checker Options

max-complexity

McCabe complexity cyclomatic threshold

Default: 10

Design checker Messages

too-complex (R1260)

%s is too complex. The McCabe rating is %d Used when a method or function is too complex based on McCabe Complexity Cyclomatic

Docstyle checker

This checker is provided by pylint.extensions.docstyle. Verbatim name of the checker is docstyle.

Docstyle checker Messages

bad-docstring-quotes (C0198)

Bad docstring quotes in %s, expected """, given %s Used when a docstring does not have triple double quotes.

docstring-first-line-empty (C0199)

First line empty in %s docstring Used when a blank line is found at the beginning of a docstring.

Else If Used checker

This checker is provided by pylint.extensions.check_elif. Verbatim name of the checker is else_if_used.

Else If Used checker Messages

else-if-used (R5501)

Consider using "elif" instead of "else if" Used when an else statement is immediately followed by an if statement and does not contain statements that would be unrelated to it.

Multiple Types checker

This checker is provided by pylint.extensions.redefined_variable_type. Verbatim name of the checker is multiple_types.

Multiple Types checker Messages

redefined-variable-type (R0204)

Redefinition of %s type from %s to %s Used when the type of a variable changes inside a method or a function.

Overlap-Except checker

This checker is provided by pylint.extensions.overlapping_exceptions. Verbatim name of the checker is overlap-except.

Overlap-Except checker Messages

overlapping-except (W0714)

Overlapping exceptions (%s) Used when exceptions in handler overlap or are identical

Parameter Documentation checker

This checker is provided by pylint.extensions.docparams. Verbatim name of the checker is parameter_documentation.

Parameter Documentation checker Documentation

If you document the parameters of your functions, methods and constructors and their types systematically in your code this optional component might be useful for you. Sphinx style, Google style, and Numpy style are supported. (For some examples, see https://pypi.python.org/pypi/sphinxcontrib-napoleon .)

You can activate this checker by adding the line:

load-plugins=pylint.extensions.docparams

to the MASTER section of your .pylintrc.

This checker verifies that all function, method, and constructor docstrings include documentation of the

  • parameters and their types

  • return value and its type

  • exceptions raised

and can handle docstrings in

  • Sphinx style (param, type, return, rtype, raise / except):

    def function_foo(x, y, z):
        '''function foo ...
    
        :param x: bla x
        :type x: int
    
        :param y: bla y
        :type y: float
    
        :param int z: bla z
    
        :return: sum
        :rtype: float
    
        :raises OSError: bla
        '''
        return x + y + z
    
  • or the Google style (Args:, Returns:, Raises:):

    def function_foo(x, y, z):
        '''function foo ...
    
        Args:
            x (int): bla x
            y (float): bla y
    
            z (int): bla z
    
        Returns:
            float: sum
    
        Raises:
            OSError: bla
        '''
        return x + y + z
    
  • or the Numpy style (Parameters, Returns, Raises):

    def function_foo(x, y, z):
        '''function foo ...
    
        Parameters
        ----------
        x: int
            bla x
        y: float
            bla y
    
        z: int
            bla z
    
        Returns
        -------
        float
            sum
    
        Raises
        ------
        OSError
            bla
        '''
        return x + y + z
    

You'll be notified of missing parameter documentation but also of naming inconsistencies between the signature and the documentation which often arise when parameters are renamed automatically in the code, but not in the documentation.

Constructor parameters can be documented in either the class docstring or the __init__ docstring, but not both:

class ClassFoo(object):
    '''Sphinx style docstring foo

    :param float x: bla x

    :param y: bla y
    :type y: int
    '''
    def __init__(self, x, y):
        pass

class ClassBar(object):
    def __init__(self, x, y):
        '''Google style docstring bar

        Args:
            x (float): bla x
            y (int): bla y
        '''
        pass

In some cases, having to document all parameters is a nuisance, for instance if many of your functions or methods just follow a common interface. To remove this burden, the checker accepts missing parameter documentation if one of the following phrases is found in the docstring:

  • For the other parameters, see

  • For the parameters, see

(with arbitrary whitespace between the words). Please add a link to the docstring defining the interface, e.g. a superclass method, after "see":

def callback(x, y, z):
    '''Sphinx style docstring for callback ...

    :param x: bla x
    :type x: int

    For the other parameters, see
    :class:`MyFrameworkUsingAndDefiningCallback`
    '''
    return x + y + z

def callback(x, y, z):
    '''Google style docstring for callback ...

    Args:
        x (int): bla x

    For the other parameters, see
    :class:`MyFrameworkUsingAndDefiningCallback`
    '''
    return x + y + z

Naming inconsistencies in existing parameter and their type documentations are still detected.

Parameter Documentation checker Options

accept-no-param-doc

Whether to accept totally missing parameter documentation in the docstring of a function that has parameters.

Default: yes

accept-no-raise-doc

Whether to accept totally missing raises documentation in the docstring of a function that raises an exception.

Default: yes

accept-no-return-doc

Whether to accept totally missing return documentation in the docstring of a function that returns a statement.

Default: yes

accept-no-yields-doc

Whether to accept totally missing yields documentation in the docstring of a generator.

Default: yes

default-docstring-type

If the docstring type cannot be guessed the specified docstring type will be used.

Default: default

Parameter Documentation checker Messages

differing-param-doc (W9017)

"%s" differing in parameter documentation Please check parameter names in declarations.

differing-type-doc (W9018)

"%s" differing in parameter type documentation Please check parameter names in type declarations.

multiple-constructor-doc (W9005)

"%s" has constructor parameters documented in class and __init__ Please remove parameter declarations in the class or constructor.

missing-param-doc (W9015)

"%s" missing in parameter documentation Please add parameter declarations for all parameters.

missing-type-doc (W9016)

"%s" missing in parameter type documentation Please add parameter type declarations for all parameters.

missing-raises-doc (W9006)

"%s" not documented as being raised Please document exceptions for all raised exception types.

useless-param-doc (W9019)

"%s" useless ignored parameter documentation Please remove the ignored parameter documentation.

useless-type-doc (W9020)

"%s" useless ignored parameter type documentation Please remove the ignored parameter type documentation.

missing-return-doc (W9011)

Missing return documentation Please add documentation about what this method returns.

missing-return-type-doc (W9012)

Missing return type documentation Please document the type returned by this method.

missing-yield-doc (W9013)

Missing yield documentation Please add documentation about what this generator yields.

missing-yield-type-doc (W9014)

Missing yield type documentation Please document the type yielded by this method.

redundant-returns-doc (W9008)

Redundant returns documentation Please remove the return/rtype documentation from this method.

redundant-yields-doc (W9010)

Redundant yields documentation Please remove the yields documentation from this method.

Refactoring checker

This checker is provided by pylint.extensions.empty_comment. Verbatim name of the checker is refactoring.

Refactoring checker Messages

empty-comment (R2044)

Line with empty comment Used when a # symbol appears on a line not followed by an actual comment

Set Membership checker

This checker is provided by pylint.extensions.set_membership. Verbatim name of the checker is set_membership.

Set Membership checker Messages

use-set-for-membership (R6201)

Consider using set for membership test Membership tests are more efficient when performed on a lookup optimized datatype like sets.

Typing checker

This checker is provided by pylint.extensions.typing. Verbatim name of the checker is typing.

Typing checker Documentation

Find issue specifically related to type annotations.

Typing checker Options

runtime-typing

Set to no if the app / library does NOT need to support runtime introspection of type annotations. If you use type annotations exclusively for type checking of an application, you're probably fine. For libraries, evaluate if some users what to access the type hints at runtime first, e.g., through typing.get_type_hints. Applies to Python versions 3.7 - 3.9

Default: yes

Typing checker Messages

deprecated-typing-alias (W6001)

'%s' is deprecated, use '%s' instead Emitted when a deprecated typing alias is used.

consider-using-alias (R6002)

'%s' will be deprecated with PY39, consider using '%s' instead%s Only emitted if 'runtime-typing=no' and a deprecated typing alias is used in a type annotation context in Python 3.7 or 3.8.

consider-alternative-union-syntax (R6003)

Consider using alternative Union syntax instead of '%s'%s Emitted when 'typing.Union' or 'typing.Optional' is used instead of the alternative Union syntax 'int | None'.

While Used checker

This checker is provided by pylint.extensions.while_used. Verbatim name of the checker is while_used.

While Used checker Messages

while-used (W0149)

Used `while` loop Unbounded while loops can often be rewritten as bounded for loops.