================== Pylint User Manual ================== :Author: Sylvain Thénault :Author: Alexandre Fayolle :Organization: Logilab .. contents:: This document is meant to be the reference user manual for Pylint_. This is a work in progress so some sections or parts may be missing (sometimes marked by a XXX). If you think it's lacking some important information, please talk about it on the python-projects mailing list (see the `Mailing lists`_ section for more information about the list). .. _Pylint: http://www.logilab.org/project/name/pylint Introduction ============ What is pylint? --------------- Pylint is a tool that checks for errors in python code, tries to enforce a coding standard and looks for smelling code. This is similar but nevertheless different from what pychecker_ provides, especially since pychecker explicitely does not bother with coding style. The default coding style used by pylint is close to `PEP 008`_ (aka `Guido's style guide`_). For more information about code smells, refer to Martin Fowler's `refactoring book`_ One important thing to note is that Pylint isn't smarter than you are: it may warn you about things that you have conscientiously done. That's for example because it tries to detect things that may be dangerous in a context, but maybe not in others, or because it checks for some things that you don't care about. Generally, you shouldn't expect pylint to be totally quiet about your code, so don't necessarily be alarmed if it gives you a hell lot of messages for your proudly(XXX) project ;) Pylint will display a number of messages as it analyzes the code, as well as some statistics about the number of warnings and errors found in different files. The messages are classified under various categories such as errors and warnings (more below). If you run pylint twice, it will display the statistics from the previous run together with the ones from the current run, so that you can see if the code has improved or not. Last but not least, the code is given an overall mark, based on the number an severity of the warnings and errors. This has proven to be very motivating for programmers. .. _pychecker: http://pychecker.sf.net .. _`PEP 008`: http://www.python.org/dev/peps/pep-0008/ .. _`Guido's style guide`: http://www.python.org/doc/essays/styleguide.html .. _`refactoring book`: http://www.refactoring.com/ Installation ------------ Dependancies '''''''''''' Pylint requires the latest `logilab-astng`_ and `logilab-common`_ packages. It should be compatible with any python version greater than 2.2.0 (python 2.2 users will have to install the optik_ package). .. _`logilab-astng`: http://www.logilab.org/project/name/astng .. _`logilab-common`: http://www.logilab.org/project/name/common .. _optik: http://optik.sourceforge.net/ Distributions ''''''''''''' The source tarball is available at ftp://ftp.logilab.fr/pub/pylint. You may apt-get a debian package by adding :: deb ftp://ftp.logilab.org/pub/debian unstable/ to your */etc/apt/sources.list* file. Pylint is also available in the standard Debian distribution (but add our public debian repository anyway if you want to get the latest releases and upgrades earlier) Contributed RPM packages for pylint and logilab-common are available at ftp://ftp.nest.pld-linux.org/test. Pylint is also available in Gentoo, Fedora 4, Ubuntu, FreeBSD, Darwin (and maybe other, if si drop us a note please!). Source distribution installation '''''''''''''''''''''''''''''''' From the source distribution, extract the tarball, go to the extracted directory and simply run :: python setup.py install You'll have to install dependancies in a similar way. Windows users may get valuable information about pylint installation on `this page`_. .. _`this page`: http://thinkhole.org/wp/2006/01/16/installing-pylint-on-windows/ Note for Windows users '''''''''''''''''''''' On Windows, once you have installed pylint, the command line usage is :: pylint.bat [options] module_or_package But this will only work if *pylint.bat* is either in the current directory, or on your system path. (*setup.py* install install *python.bat* to the *Scripts* subdirectory of your Python installation -- e.g. C:\Python24\Scripts.) You can do any of the following to solve this: 1. change to the appropriate directory before running pylint.bat 2. add the Scripts directory to your path statement in your autoexec.bat file (this file is found in the root directory of your boot-drive) 3. create a 'redirect' batch file in a directory actually on your systems path To effect (2), simply append the appropriate directory name to the PATH= statement in autoexec.bat. Be sure to use the Windows directory separator of ';' between entries. Then, once you have rebooted (this is necessary so that the new path statement will take effect when autoexec.bat is run), you will be able to invoke PyLint with pylint.bat on the command line. (3) is the best solution. Once done, you can call pylint at the command line without the .bat, just as do non-Windows users by typing: :: pylint [options] module_or_package To effect option (3), simply create a plain text file pylint.bat with the single line: :: C:\PythonDirectory\Scripts\pylint.bat (where PythonDirectory is replaced by the actual Python installation directory on your system -- e.g. C:\Python24\Scripts\pylint.bat). Invoking pylint --------------- Pylint is meant to be called from the command line. The usage is :: pylint [options] module_or_package You should give pylint the name of a Python package or module. Pylint will ``import`` this package or module, so you should pay attention to your ``PYTHONPATH``, since it is a common error to analyze an installed version of a module instead of the development version. It is also possible to analyze python files, with a few restriction. The thing to keep in mind is that pylint will try to convert the file name to a module name, and only be able to process the file if it succeeds. :: pylint mymodule.py should always work since the current working directory is automatically added on top of the python path :: pylint directory/mymodule.py will work if "directory" is a python package (i.e. has an __init__.py file) or if "directory" is in the python path. For more details on this see the `Frequently Asked Questions`_. You can also start a thin gui around pylint (require TkInter) by typing :: pylint-gui This should open a window where you can enter the name of the package or module to check, at pylint messages will be displayed in the user interface. Pylint output ------------- The default format for the output is raw text. But passing pylint the ``--html`` option will produce an HTML document. There are several sections in pylint's output. Source code analysis section '''''''''''''''''''''''''''' For each python module, pylint will first display a few '*' characters followed by the name of the module. Then, a number of messages with the following format: :: MESSAGE_TYPE: LINE_NUM:[OBJECT:] MESSAGE You can get another output format, useful since it's recognized by most editors or other development tools using the ``--parseable=y`` option. The message type can be: * [R]efactor for a "good practice" metric violation * [C]onvention for coding standard violation * [W]arning for stylistic problems, or minor programming issues * [E]rror for important programming issues (i.e. most probably bug) * [F]atal for errors which prevented further processing Sometimes the line of code which caused the error is displayed with a caret pointing to the error. This may be generalized in future versions of pylint. Example (extracted from a run of pylint on itself...): :: ************* Module pylint.checkers.format W: 50: Too long line (86/80) W:108: Operator not followed by a space print >>sys.stderr, 'Unable to match %r', line ^ W:141: Too long line (81/80) W: 74:searchall: Unreachable code W:171:FormatChecker.process_tokens: Redefining built-in (type) W:150:FormatChecker.process_tokens: Too many local variables (20/15) W:150:FormatChecker.process_tokens: Too many branchs (13/12) Reports section ''''''''''''''' Following the analysis message, pylint will display a set of reports, each one focusing on a particular aspect of the project, such as number of messages by categories, modules dependancies... For instance, the metrics report displays summaries gathered from the current run. * the number of processed modules * for each module, the percentage of errors and warnings * the total number of errors and warnings * percentage of classes, functions and modules with docstrings, and a comparison from the previous run * percentage of classes, functions and modules with correct name (according the the coding standard), and a comparison from the previous run * a list of external dependencies found in the code, and where they appear Also, a global evaluation for the code is computed, and an optional witty comment is displayed (if ``--comment=y`` was specified on the command line). Command line options -------------------- First of all, we have two basic (but useful) options. --version show program's version number and exit -h, --help show help about the command line options Pylint is architectured around several checkers. By default all checkers are enabled. You can disable a specific checker by specifying ``--enable-=n``, or disable all checkers using ``--disable-all`` and afterwards enable specific checkers with ``--enable-=y``. See the list of available features_ for a description of provided checkers with their functionalities. Each checker has some specific options, which can take either a yes/no value, an integer, a python regular expression, or a comma separated list of values (which are generally used to override a regular expression in special cases). For a full list of options, use ``--help`` Specifying all the options suitable for your setup and coding standards can be tedious, so it is possible to use a rc file to specify the default values. Pylint looks for /etc/pylintrc and ~/.pylintrc. The ``--generate-rcfile`` option will generate a commented configuration file according to the current configuration on standard output and exit. You can put other options before this one to use them in the configuration, or start with the default values and hand tune the configuration. Other useful global options include: --zope Initialize Zope products before starting --ignore=file Add (may be a directory) to the black list. It should be a base name, not a path. You may set this option multiple times. --statistics=y_or_n Compute statistics on collected data. --persistent=y_or_n Pickle collected data for later comparisons. --comment=y_or_n Add a comment according to your evaluation note. --parseable=y_or_n Use a parseable output format. --html=y_or_n Use HTML as output format instead of text. --enable-msg=msgids Enable the given messages. --disable-msg=msgids Disable the given messages. --enable-msg-cat=cats Enable all messages in the given categories. --disable-msg-cat=cats Disable all messages in the given categories. --errors-only Enable only checkers from the error category. .. _features: features.html Daily pylint usage ------------------ What pylint says is not to be taken as gospel. While getting as few false positives for errors as possible is a goal for us -- and python makes it hard enough, it is not the case for warnings. :Quoting Alexandre: My usage pattern for pylint is to generally run pylint -e quite often to get stupid errors flagged before launching an application (or before comitting). I generally run pylint with all the bells and whistles activated some time before a release, when I want to cleanup the code. And when I do that I simply ignore tons of the false warnings (and I can do that without being driven mad by this dumb program which is not smart enough to understand the dynamicity of Python because I only run it once or twice a week in this mode) :Quoting Marteen Ter Huurne: In our project we just accepted that we have to make some modifications in our code to please PyLint: - stick to more naming conventions (unused variables ending in underscores, mix-in class names ending in "Mixin") - making all abstract methods explicit (rather than just not defining them in the superclass) - for messages which are useful in general, but not in a specific case: add "# pylint: disable-msg=X0123" comments - for PyLint bugs: add "#pylint: disable-msg=X0123" comments - for PyLint limitations: add "#pylint: disable-msg=X0123" comments (for instance Twisted's modules create a lot of definitions dynamically so PyLint does not know about them) The effort is worth it, since PyLint helps us a lot in keeping the code clean and finding errors early. Although most errors found by PyLint would also be found by the regression tests, by fixing them before committing, we save time. And our regression tests do not cover all code either, just the most complex parts. Bug reports, feedback --------------------- You think you have found a bug in Pylint? Well, this may be the case since Pylint is under development. Please take the time to send a bug report to python-projects@logilab.org if you've not found it already reported on the `tracker page`_. This mailing list is also a nice place to discuss Pylint issues, see below for more information about pylint's related lists. You can check for already reported bugs, planned features on pylint's tracker web page: http://www.logilab.org/project/name/pylint Notice that if you don't find something you have expected in pylint's tracker page, it may be on the tracker page of one of its dependancies, namely astng and common: * http://www.logilab.org/project/name/logilab-astng * http://www.logilab.org/project/name/logilab-common .. _`tracker page`: http://www.logilab.org/project/name/pylint Mailing lists ------------- Use the python-projects@logilab.org mailing list for anything related to Pylint. This is in most cases better than sending an email directly to the author, since others will benefit from the exchange, and you'll be more likely answered by someone subscribed to the list. This is a moderated mailing list, so if you're not subscribed email you send will have to be validated first before actually being sent on the list. You can subscribe to this mailing list at http://lists.logilab.org/mailman/listinfo/python-projects Archives are available at http://lists.logilab.org/pipermail/python-projects/ If you prefer speaking french instead of english, you can use the generic forum-fr@logilab.org mailing list: * (un)subscribe: http://lists.logilab.org/mailman/listinfo/forum-fr * archives: http://lists.logilab.org/pipermail/forum-fr Notice though that this list has a very low traffic since most pylint related discussions are done on the python-projects mailing list. Advanced usage ============== Base configuration ------------------ To be written... Environment ----------- To be written... Messages control ---------------- An example available from the examples directory:: """pylint option block-disable-msg""" __revision__ = None class Foo(object): """block-disable-msg test""" def __init__(self): pass def meth1(self, arg): """this issues a message""" print self def meth2(self, arg): """and this one not""" # pylint: disable-msg=W0613 print self\ + "foo" def meth3(self): """test one line disabling""" # no error print self.bla # pylint: disable-msg=E1101 # error print self.blop def meth4(self): """test re-enabling""" # pylint: disable-msg=E1101 # no error print self.bla print self.blop # pylint: enable-msg=E1101 # error print self.blip def meth5(self): """test IF sub-block re-enabling""" # pylint: disable-msg=E1101 # no error print self.bla if self.blop: # pylint: enable-msg=E1101 # error print self.blip else: # no error print self.blip # no error print self.blip def meth6(self): """test TRY/EXCEPT sub-block re-enabling""" # pylint: disable-msg=E1101 # no error print self.bla try: # pylint: enable-msg=E1101 # error print self.blip except UndefinedName: # pylint: disable-msg=E0602 # no error print self.blip # no error print self.blip def meth7(self): """test one line block opening disabling""" if self.blop: # pylint: disable-msg=E1101 # error print self.blip else: # error print self.blip # error print self.blip def meth8(self): """test late disabling""" # error print self.blip # pylint: disable-msg=E1101 # no error print self.bla print self.blop About analysis ============== Pylint heuristics ----------------- To be written... About astng inference --------------------- To be written... Enhancing Pylint ================ Writing your own checker ------------------------ You can find some simple examples in the examples directory of the distribution (custom.py and custom_raw.py). I'll try to quickly explain the essentials here. First, there are two kinds of checkers : * raw checkers, which are analysing each module as a raw file stream * ast checkers, which are working on an ast representation of the module The ast representation used is an extension of the one provided with the standard python distribution in the `compiler package`_. The extension adds additional information and methods on the tree nodes to ease navigation and code introspection. An AST checker is a visitor, and should implement visit_ leave_ methods for the nodes it's interested in. To get description of the different classes used in an ast tree, look at the `compiler.ast documentation`. Checkers are ordered by priority. For each module, pylint's engine: 1. give the module source file as a stream to raw checkers 2. get an ast representation for the module 3. make a depth first descent of the tree, calling visit_<> on each AST checker when entering a node, and living_<> on the back traversal Notice that the source code is probably the best source of documentation, it should be clear and well documented. Don't hesitate to ask for any information on the python-projects mailing list. .. _`compiler package`: http://python.org/doc/current/lib/module-compiler.html .. _`compiler.ast documentation`: http://www.python.org/doc/current/lib/module-compiler.ast.html Contribute ! ------------ All our software is developped using the mercurial_ version control system. This is a very cool distributed vcs and its usage is very similar to other ones such as cvs or subversion (though the distributed feature introduced some different usage patterns). See mercurial home page for installation on your computer and basic usage. Note that it's very easy to send us patches using `hg email` command ;). You can get the in-development pylint source code from our public mercurial_ repository: http://www.logilab.org/src/pylint The same is true for pylint dependancies (if you use pylint code from the repository, you should usually use code from the repository as well for astng and common): http://www.logilab.org/src/logilab/astng http://www.logilab.org/src/logilab/common .. _mercurial: http://www.selenic.com/mercurial/ Other information ================= IDE integration --------------- Pylint is integrated in the following editors/IDEs: * emacs (of course) * eric3 * eclipse (using the pydev_ plugin, see also http://msdl.cs.mcgill.ca/MSDL/people/denis/meetings/pythonDev) To use pylint from within vim, see http://www.gonzo.kiev.ua/projects/pylint.vim To use pylint from within komodo_, see http://mateusz.loskot.net/2006/01/15/running-pylint-from-komodo/ To use pylint from within gedit_, see http://live.gnome.org/Gedit/PylintPlugin .. _pydev: http://pydev.sourceforge.net .. _komodo: http://www.activestate.com/Products/Komodo/ .. _gedit: http://www.gnome.org/projects/gedit/ Some projects using Pylint -------------------------- The following projects are known to use pylint to help develop better code: * OSAF Chandler (http://www.osafoundation.org/) * Xen (http://www.xensource.com/) * CPS (http://www.nuxeo.org) * ERP5 (http://www.erp5.org/) * pyxmpp (http://pyxmpp.jabberstudio.org/) * mercurial * eXe (http://exelearning.org/) * PrimaGIS (http://www.primagis.org) * python-cdd (http://projetos.ossystems.com.br/python-cdd/) * CDSWare (http://cdsware.cern.ch/) * ASE (http://dcwww.camp.dtu.dk/campos/ASE/intro.html) * RunJob (http://projects.fnal.gov/runjob/) * Slugathon (http://slugathon.python-hosting.com/) * Topographica (http://topographica.org/Home/index.html) (at least they intend to do so) * http://browsershots.org * many more... Also notice that the CheeseCake_ kwalitee reporting tool uses pylint to analyze the source code. .. _CheeseCake: http://cheesecake.sourceforge.net/ .. include:: FAQ.txt