path: root/doc/features.txt

PyLint features
===============

.. contents::

General options
~~~~~~~~~~~~~~~
:rcfile:
  Specify a configuration file.
:init-hook:
  Python code to execute, usually for sys.path manipulation such as
  pygtk.require().
:rpython-mode:
  enable the rpython checker which is disabled by default
:errors-only:
  In debug mode, checkers without error messages are disabled and for others,
  only the ERROR messages are displayed, and no reports are done by default
:profile:
  Profiled execution.
:ignore:
  Add <file or directory> to the black list. It should be a base name, not a
  path. You may set this option multiple times.
  Default: CVS
:persistent:
  Pickle collected data for later comparisons.
  Default: yes
:cache-size:
  Set the cache size for astng objects.
  Default: 500
:load-plugins:
  List of plugins (as comma separated values of python modules names) to load,
  usually to register additional checkers.

Commands options
~~~~~~~~~~~~~~~~
:help-msg:
  Display a help message for the given message id and exit. The value may be a
  comma separated list of message ids.
:list-msgs:
  Generate pylint's full documentation.
:generate-rcfile:
  Generate a sample configuration file according to the current configuration.
  You can put other options before this one to get them in the generated
  configuration.
:generate-man:
  Generate pylint's man page.

Messages control options
~~~~~~~~~~~~~~~~~~~~~~~~
:enable-checker:
  Enable only checker(s) with the given id(s). This option conflicts with the
  disable-checker option
:disable-checker:
  Enable all checker(s) except those with the given id(s). This option
  conflicts with the enable-checker option
:enable-msg-cat:
  Enable all messages in the listed categories.
:disable-msg-cat:
  Disable all messages in the listed categories.
:enable-msg:
  Enable the message(s) with the given id(s).
:disable-msg:
  Disable the message(s) with the given id(s).

Reports options
~~~~~~~~~~~~~~~
:output-format:
  Set the output format. Available formats are text, parseable, colorized, msvs
  (visual studio) and html
  Default: text
:include-ids:
  Include message's id in output
:files-output:
  Put messages in a separate file for each module / package specified on the
  command line instead of printing them on stdout. Reports (if any) will be
  written in a file name "pylint_global.[txt|html]".
:reports:
  Tells wether to display a full report or only the messages
  Default: yes
:evaluation:
  Python expression which should return a note less than 10 (10 is the highest
  note). You have access to the variables errors warning, statement which
  respectivly contain the number of errors / warnings messages and the total
  number of statements analyzed. This is used by the global evaluation report
  (R0004).
  Default: 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10)
:comment:
  Add a comment according to your evaluation note. This is used by the global
  evaluation report (R0004).
:enable-report:
  Enable the report(s) with the given id(s).
:disable-report:
  Disable the report(s) with the given id(s).

Main messages
~~~~~~~~~~~~~
:E0001:
  Used when a syntax error is raised for a module.
:E0011: *Unrecognized file option %r*
  Used when an unknown inline option is encountered.
:E0012: *Bad option value %r*
  Used when a bad value for an inline option is encountered.
:I0001: *Unable to run raw checkers on built-in module %s*
  Used to inform that a built-in module has not been checked using the raw
  checkers.
:I0010: *Unable to consider inline option %r*
  Used when an inline option is either badly formatted or can't be used inside
  modules.
:I0011: *Locally disabling %s*
  Used when an inline option disables a message or a messages category.
:I0012: *Locally enabling %s*
  Used when an inline option enables a message or a messages category.
:I0013: *Ignoring entire file*
  Used to inform that the file will not be checked
:F0001:
  Used when an error occured preventing the analysis of a module (unable to find
  it for instance).
:F0002: *%s: %s*
  Used when an unexpected error occured while building the ASTNG representation.
  This is usually accompanied by a traceback. Please report such errors !
:F0003: *ignored builtin module %s*
  Used to indicate that the user asked to analyze a builtin module which has
  been skipped.
:F0004: *unexpected infered value %s*
  Used to indicate that some value of an unexpected type has been infered.

Main reports
~~~~~~~~~~~~
:R0001: Messages by category
:R0002: % errors / warnings by module
:R0003: Messages
:R0004: Global evaluation


Basic checker
-------------
checks for :
* doc strings
* modules / classes / functions / methods / arguments / variables name
* number of arguments, local variables, branchs, returns and statements in
functions, methods
* required module attributes
* dangerous default values as arguments
* redefinition of function / method / class
* uses of the global statement

Options
~~~~~~~
:required-attributes:
  Required attributes for module, separated by a comma
:no-docstring-rgx:
  Regular expression which should only match functions or classes name which do
  not require a docstring
  Default: __.*__
:module-rgx:
  Regular expression which should only match correct module names
  Default: (([a-z_][a-z0-9_]*)|([A-Z][a-zA-Z0-9]+))$
:const-rgx:
  Regular expression which should only match correct module level names
  Default: (([A-Z_][A-Z1-9_]*)|(__.*__))$
:class-rgx:
  Regular expression which should only match correct class names
  Default: [A-Z_][a-zA-Z0-9]+$
:function-rgx:
  Regular expression which should only match correct function names
  Default: [a-z_][a-z0-9_]{2,30}$
:method-rgx:
  Regular expression which should only match correct method names
  Default: [a-z_][a-z0-9_]{2,30}$
:attr-rgx:
  Regular expression which should only match correct instance attribute names
  Default: [a-z_][a-z0-9_]{2,30}$
:argument-rgx:
  Regular expression which should only match correct argument names
  Default: [a-z_][a-z0-9_]{2,30}$
:variable-rgx:
  Regular expression which should only match correct variable names
  Default: [a-z_][a-z0-9_]{2,30}$
:inlinevar-rgx:
  Regular expression which should only match correct list comprehension /
  generator expression variable names
  Default: [A-Za-z_][A-Za-z0-9_]*$
:good-names:
  Good variable names which should always be accepted, separated by a comma
  Default: i,j,k,ex,Run,_
:bad-names:
  Bad variable names which should always be refused, separated by a comma
  Default: foo,bar,baz,toto,tutu,tata
:bad-functions:
  List of builtins function names that should not be used, separated by a comma
  Default: map,filter,apply,input

Messages
~~~~~~~~
:E0100: *__init__ method is a generator*
  Used when the special class method __init__ is turned into a generator by a
  yield in its body.
:E0101: *Explicit return in __init__*
  Used when the special class method __init__ has an explicit return value.
:E0102: *%s already defined line %s*
  Used when a function / class / method is redefined.
:E0103: *%r not properly in loop*
  Used when break or continue keywords are used outside a loop.
:E0104: *return outside function*
  Used when a "return" statement is found outside a function or method.
:E0105: *yield outside function*
  Used when a "yield" statement is found outside a function or method.
:E0106: *return with argument inside generator*
  Used when a "return" statement with an argument is found outside in a
  generator function or method (e.g. with some "yield" statements).
:W0101: *Unreachable code*
  Used when there is some code behind a "return" or "raise" statement, which
  will never be accessed.
:W0102: *Dangerous default value %s as argument*
  Used when a mutable value as list or dictionary is detected in a default value
  for an argument.
:W0104: *Statement seems to have no effect*
  Used when a statement doesn't have (or at least seems to) any effect.
:W0105: *String statement has no effect*
  Used when a string is used as a statement (which of course has no effect).
  This is a particular case of W0104 with its own message so you can easily
  disable it if you're using those strings as documentation, instead of
  comments.
:W0106: *Unnecessary semicolon*
  Used when a statement is endend by a semi-colon (";"), which isn't necessary
  (that's python, not C ;).
:W0107: *Unnecessary pass statement*
  Used when a "pass" statement that can be avoided is encountered.)
:W0122: *Use of the exec statement*
  Used when you use the "exec" statement, to discourage its usage. That doesn't
  mean you can not use it !
:W0141: *Used builtin function %r*
  Used when a black listed builtin function is used (see the bad-function
  option). Usual black listed functions are the ones like map, or filter , where
  Python offers now some cleaner alternative like list comprehension.
:W0142: *Used * or ** magic*
  Used when a function or method is called using `*args` or `**kwargs` to
  dispatch arguments. This doesn't improve readability and should be used with
  care.
:C0102: *Black listed name "%s"*
  Used when the name is listed in the black list (unauthorized names).
:C0103: *Invalid name "%s" (should match %s)*
  Used when the name doesn't match the regular expression associated to its type
  (constant, variable, class...).
:C0111: *Missing docstring*
  Used when a module, function, class or method has no docstring. Some special
  methods like __init__ doesn't necessary require a docstring.
:C0112: *Empty docstring*
  Used when a module, function, class or method has an empty docstring (it would
  be too easy ;).
:C0121: *Missing required attribute "%s"*
  Used when an attribute required for modules is missing.

Reports
~~~~~~~
:R0101: Statistics by type


Typecheck checker
-----------------
try to find bugs in the code using type inference

Options
~~~~~~~
:ignore-mixin-members:
  Tells wether missing members accessed in mixin class should be ignored. A
  mixin class is detected if its name ends with "mixin" (case insensitive).
  Default: yes
:ignored-classes:
  List of classes names for which member attributes should not be checked
  (useful for classes with attributes dynamicaly set).
  Default: SQLObject
:zope:
  When zope mode is activated, consider the acquired-members option to ignore
  access to some undefined attributes.
:acquired-members:
  List of members which are usually get through zope's acquisition mecanism and
  so shouldn't trigger E0201 when accessed (need zope=yes to be considered).
  Default: REQUEST,acl_users,aq_parent

Messages
~~~~~~~~
:E1101: *%s %r has no %r member*
  Used when a variable is accessed for an unexistant member.
:E1102: *%s is not callable*
  Used when an object being called has been infered to a non callable object
:E1103: *%s %r has no %r member (but some types could not be inferred)*
  Used when a variable is accessed for an unexistant member, but astng was not
  able to interpret all possible types of this variable.
:E1111: *Assigning to function call which doesn't return*
  Used when an assigment is done on a function call but the infered function
  doesn't return anything.
:W1111: *Assigning to function call which only returns None*
  Used when an assigment is done on a function call but the infered function
  returns nothing but None.


Variables checker
-----------------
checks for
* unused variables / imports
* undefined variables
* redefinition of variable from builtins or from an outer scope
* use of variable before assigment

Options
~~~~~~~
:init-import:
  Tells wether we should check for unused import in __init__ files.
:dummy-variables-rgx:
  A regular expression matching names used for dummy variables (i.e. not used).
  Default: _|dummy
:additional-builtins:
  List of additional names supposed to be defined in builtins. Remember that
  you should avoid to define new builtins when possible.

Messages
~~~~~~~~
:E0601: *Using variable %r before assignment*
  Used when a local variable is accessed before it's assignment.
:E0602: *Undefined variable %r*
  Used when an undefined variable is accessed.
:E0611: *No name %r in module %r*
  Used when a name cannot be found in a module.
:W0601: *Global variable %r undefined at the module level*
  Used when a variable is defined through the "global" statement but the
  variable is not defined in the module scope.
:W0602: *Using global for %r but no assigment is done*
  Used when a variable is defined through the "global" statement but no
  assigment to this variable is done.
:W0603: *Using the global statement*
  Used when you use the "global" statement to update a global variable. PyLint
  just try to discourage this usage. That doesn't mean you can not use it !
:W0604: *Using the global statement at the module level*
  Used when you use the "global" statement at the module level since it has no
  effect
:W0611: *Unused import %s*
  Used when an imported module or variable is not used.
:W0612: *Unused variable %r*
  Used when a variable is defined but not used.
:W0613: *Unused argument %r*
  Used when a function or method argument is not used.
:W0614: *Unused import %s from wildcard import*
  Used when an imported module or variable is not used from a 'from X import *'
  style import.
:W0621: *Redefining name %r from outer scope (line %s)*
  Used when a variable's name hide a name defined in the outer scope.
:W0622: *Redefining built-in %r*
  Used when a variable or function override a built-in.
:W0631: *Using possibly undefined loop variable %r*
  Used when an loop variable (i.e. defined by a for loop or a list comprehension
  or a generator expression) is used outside the loop.


Classes checker
---------------
checks for :
* methods without self as first argument
* overridden methods signature
* access only to existant members via self
* attributes not defined in the __init__ method
* supported interfaces implementation
* unreachable code

Options
~~~~~~~
:ignore-iface-methods:
  List of interface methods to ignore, separated by a comma. This is used for
  instance to not check methods defines in Zope's Interface base class.
  Default: isImplementedBy,deferred,extends,names,namesAndDescriptions,queryDescriptionFor,getBases,getDescriptionFor,getDoc,getName,getTaggedValue,getTaggedValueTags,isEqualOrExtendedBy,setTaggedValue,isImplementedByInstancesOf,adaptWith,is_implemented_by
:defining-attr-methods:
  List of method names used to declare (i.e. assign) instance attributes.
  Default: __init__,__new__,setUp

Messages
~~~~~~~~
:E0202: *An attribute inherited from %s hide this method*
  Used when a class defines a method which is hiden by an instance attribute
  from an ancestor class.
:E0203: *Access to member %r before its definition line %s*
  Used when an instance member is accessed before it's actually assigned.
:E0211: *Method has no argument*
  Used when a method which should have the bound instance as first argument has
  no argument defined.
:E0213: *Method should have "self" as first argument*
  Used when a method has an attribute different the "self" as first argument.
  This is considered as an error since this is a soooo common convention that
  you should'nt break it!
:E0221: *Interface resolved to %s is not a class*
  Used when a class claims to implement an interface which is not a class.
:E0222: *Missing method %r from %s interface*
  Used when a method declared in an interface is missing from a class
  implementing this interface
:W0201: *Attribute %r defined outside __init__*
  Used when an instance attribute is defined outside the __init__ method.
:W0211: *Static method with %r as first argument*
  Used when a static method has "self" or "cls" as first argument.
:W0212: *Access to a protected member %s of a client class*
  Used when a protected member (i.e. class member with a name beginning with an
  underscore) is access outside the class or a descendant of the class where
  it's defined.
:W0221: *Arguments number differs from %s method*
  Used when a method has a different number of arguments than in the implemented
  interface or in an overridden method.
:W0222: *Signature differs from %s method*
  Used when a method signature is different than in the implemented interface or
  in an overridden method.
:W0223: *Method %r is abstract in class %r but is not overridden*
  Used when an abstract method (ie raise NotImplementedError) is not overridden
  in concrete class.
:W0231: *__init__ method from base class %r is not called*
  Used when an ancestor class method has an __init__ method which is not called
  by a derived class.
:W0232: *Class has no __init__ method*
  Used when a class has no __init__ method, neither its parent classes.
:W0233: *__init__ method from a non direct base class %r is called*
  Used when an __init__ method is called on a class which is not in the direct
  ancestors for the analysed class.
:R0201: *Method could be a function*
  Used when a method doesn't use its bound instance, and so could be written as
  a function.
:C0202: *Class method should have "cls" as first argument*
  Used when a class method has an attribute different than "cls" as first
  argument, to easily differentiate them from regular instance methods.
:C0203: *Metaclass method should have "mcs" as first argument*
  Used when a metaclass method has an attribute different the "mcs" as first
  argument.
:F0202: *Unable to check methods signature (%s / %s)*
  Used when PyLint has been unable to check methods signature compatibility for
  an unexpected raison. Please report this kind if you don't make sense of it.
:F0220: *failed to resolve interfaces implemented by %s (%s)*
  Used when a PyLint as failed to find interfaces implemented by a class


Design checker
--------------
checks for sign of poor/misdesign:
* number of methods, attributes, local variables...
* size, complexity of functions, methods

Options
~~~~~~~
:max-args:
  Maximum number of arguments for function / method
  Default: 5
:max-locals:
  Maximum number of locals for function / method body
  Default: 15
:max-returns:
  Maximum number of return / yield for function / method body
  Default: 6
:max-branchs:
  Maximum number of branch for function / method body
  Default: 12
:max-statements:
  Maximum number of statements in function / method body
  Default: 50
:max-parents:
  Maximum number of parents for a class (see R0901).
  Default: 7
:max-attributes:
  Maximum number of attributes for a class (see R0902).
  Default: 7
:min-public-methods:
  Minimum number of public methods for a class (see R0903).
  Default: 2
:max-public-methods:
  Maximum number of public methods for a class (see R0904).
  Default: 20

Messages
~~~~~~~~
:R0901: *Too many ancestors (%s/%s)*
  Used when class has too many parent classes, try to reduce this to get a more
  simple (and so easier to use) class.
:R0902: *Too many instance attributes (%s/%s)*
  Used when class has too many instance attributes, try to reduce this to get a
  more simple (and so easier to use) class.
:R0903: *Too few public methods (%s/%s)*
  Used when class has too few public methods, so be sure it's really worth it.
:R0904: *Too many public methods (%s/%s)*
  Used when class has too many public methods, try to reduce this to get a more
  simple (and so easier to use) class.
:R0911: *Too many return statements (%s/%s)*
  Used when a function or method has too many return statement, making it hard
  to follow.
:R0912: *Too many branches (%s/%s)*
  Used when a function or method has too many branches, making it hard to
  follow.
:R0913: *Too many arguments (%s/%s)*
  Used when a function or method takes too many arguments.
:R0914: *Too many local variables (%s/%s)*
  Used when a function or method has too many local variables.
:R0915: *Too many statements (%s/%s)*
  Used when a function or method has too many statements. You should then split
  it in smaller functions / methods.
:R0921: *Abstract class not referenced*
  Used when an abstract class is not used as ancestor anywhere.
:R0922: *Abstract class is only referenced %s times*
  Used when an abstract class is used less than X times as ancestor.
:R0923: *Interface not implemented*
  Used when an interface class is not implemented anywhere.


Imports checker
---------------
checks for
* external modules dependencies
* relative / wildcard imports
* cyclic imports
* uses of deprecated modules

Options
~~~~~~~
:deprecated-modules:
  Deprecated modules which should not be used, separated by a comma
  Default: regsub,string,TERMIOS,Bastion,rexec
:import-graph:
  Create a graph of every (i.e. internal and external) dependencies in the
  given file (report R0402 must not be disabled)
:ext-import-graph:
  Create a graph of external dependencies in the given file (report R0402 must
  not be disabled)
:int-import-graph:
  Create a graph of internal dependencies in the given file (report R0402 must
  not be disabled)

Messages
~~~~~~~~
:W0401: *Wildcard import %s*
  Used when `from module import *` is detected.
:W0402: *Uses of a deprecated module %r*
  Used a module marked as deprecated is imported.
:W0403: *Relative import %r*
  Used when an import relative to the package directory is detected.
:W0404: *Reimport %r (imported line %s)*
  Used when a module is reimported multiple times.
:W0406: *Module import itself*
  Used when a module is importing itself.
:W0410: *__future__ import is not the first non docstring statement*
  Python 2.5 and greater require __future__ import to be the first non docstring
  statement in the module.
:R0401: *Cyclic import (%s)*
  Used when a cyclic import between two or more modules is detected.
:F0401: *Unable to import %r (%s)*
  Used when pylint has been unable to import a module.

Reports
~~~~~~~
:R0401: External dependencies
:R0402: Modules dependencies graph


Newstyle checker
----------------
checks for usage of new style capabilities on old style classes and
other new/old styles conflicts problems
* use of property, __slots__, super
* "super" usage
* raising a new style class as exception

Messages
~~~~~~~~
:E1001: *Use __slots__ on an old style class*
  Used when an old style class use the __slots__ attribute.
:E1002: *Use super on an old style class*
  Used when an old style class use the super builtin.
:E1003: *Bad first argument %r given to super class*
  Used when another argument than the current class is given as first argument
  of the super builtin.
:E1010: *Raising a new style class*
  Used when a new style class is raised since it's not possible with python <
  2.5.
:W1001: *Use of "property" on an old style class*
  Used when PyLint detect the use of the builtin "property" on an old style
  class while this is relying on new style classes features
:W1010: *Exception doesn't inherit from standard "Exception" class*
  Used when a custom exception class is raised but doesn't inherit from the
  builtin "Exception" class.


Exceptions checker
------------------
checks for
* excepts without exception filter
* string exceptions

Messages
~~~~~~~~
:E0701: *Bad except clauses order (%s)*
  Used when except clauses are not in the correct order (from the more specific
  to the more generic). If you don't fix the order, some exceptions may not be
  catched by the most specific handler.
:E0702: *Raising %s while only classes, instances or string are allowed*
  Used when something which is neither a class, an instance or a string is
  raised (i.e. a `TypeError` will be raised).
:W0701: *Raising a string exception*
  Used when a string exception is raised.
:W0702: *No exception type(s) specified*
  Used when an except clause doesn't specify exceptions type to catch.
:W0703: *Catch "Exception"*
  Used when an except catches Exception instances.
:W0704: *Except doesn't do anything*
  Used when an except clause does nothing but "pass" and there is no "else"
  clause.
:W0706: *Identifier %s used to raise an exception is assigned to %s*
  Used when a variable used to raise an exception is initially assigned to a
  value which can't be used as an exception.


Format checker
--------------
checks for :
* unauthorized constructions
* strict indentation
* line length
* use of <> instead of !=

Options
~~~~~~~
:max-line-length:
  Maximum number of characters on a single line.
  Default: 80
:max-module-lines:
  Maximum number of lines in a module
  Default: 1000
:indent-string:
  String used as indentation unit. This is usually " " (4 spaces) or "\t" (1
  tab).
  Default: '    '

Messages
~~~~~~~~
:W0311: *Bad indentation. Found %s %s, expected %s*
  Used when an unexpected number of indentation's tabulations or spaces has been
  found.
:W0312: *Found indentation with %ss instead of %ss*
  Used when there are some mixed tabs and spaces in a module.
:W0331: *Use of the <> operator*
  Used when the deprecated "<>" operator is used instead of "!=".
:W0332: *Use l as long integer identifier*
  Used when a lower case "l" is used to mark a long integer. You should use a
  upper case "L" since the letter "l" looks too much like the digit "1"
:W0333: *Use of the `` operator*
  Used when the deprecated "``" (backtick) operator is used instead of the str()
  function.
:C0301: *Line too long (%s/%s)*
  Used when a line is longer than a given number of characters.
:C0302: *Too many lines in module (%s)*
  Used when a module has too much lines, reducing its readibility.
:C0321: *More than one statement on a single line*
  Used when more than on statement are found on the same line.
:C0322: *Operator not preceded by a space*
  Used when one of the following operator (!= | <= | == | >= | < | > | = | \+= |
  -= | \*= | /= | %) is not preceded by a space.
:C0323: *Operator not followed by a space*
  Used when one of the following operator (!= | <= | == | >= | < | > | = | \+= |
  -= | \*= | /= | %) is not followed by a space.
:C0324: *Comma not followed by a space*
  Used when a comma (",") is not followed by a space.
:F0321: *Format detection error in %r*
  Used when an unexpected error occured in bad format detection.Please report
  the error if it occurs.


Miscellaneous checker
---------------------
checks for:
* warning notes in the code like FIXME, XXX
* PEP 263: source code with non ascii character but no encoding declaration

Options
~~~~~~~
:notes:
  List of note tags to take in consideration, separated by a comma.
  Default: FIXME,XXX,TODO

Messages
~~~~~~~~
:E0501: *Non ascii characters found but no encoding specified (PEP 263)*
  Used when some non ascii characters are detected but now encoding is
  specified, as explicited in the PEP 263.
:E0502: *Wrong encoding specified (%s)*
  Used when a known encoding is specified but the file doesn't seem to be
  actually in this encoding.
:E0503: *Unknown encoding specified (%s)*
  Used when an encoding is specified, but it's unknown to Python.
:W0511:
  Used when a warning note as FIXME or XXX is detected.


Metrics checker
---------------
does not check anything but gives some raw metrics :
* total number of lines
* total number of code lines
* total number of docstring lines
* total number of comments lines
* total number of empty lines

Reports
~~~~~~~
:R0701: Raw metrics


Similarities checker
--------------------
checks for similarities and duplicated code. This computation may be
memory / CPU intensive, so you should disable it if you experiments some
problems.

Options
~~~~~~~
:min-similarity-lines:
  Minimum lines number of a similarity.
  Default: 4
:ignore-comments:
  Ignore comments when computing similarities.
  Default: yes
:ignore-docstrings:
  Ignore docstrings when computing similarities.
  Default: yes

Messages
~~~~~~~~
:R0801: *Similar lines in %s files*
  Indicates that a set of similar lines has been detected among multiple file.
  This usually means that the code should be refactored to avoid this
  duplication.

Reports
~~~~~~~
:R0801: Duplication