| 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 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.
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).
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!).
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.
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:Python24Scripts.) You can do any of the following to solve this:
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:Python24Scriptspylint.bat).
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.
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.
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)
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).
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-<checker>=n, or disable all checkers using --disable-all and afterwards enable specific checkers with --enable-<checker>=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 <file> (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. |
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:
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. |
|
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:
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:
Notice though that this list has a very low traffic since most pylint related discussions are done on the python-projects mailing list.
To be written...
To be written...
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
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_<lowered class name> leave_<lowered class name> 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:
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.
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
Pylint is integrated in the following editors/IDEs:
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
The following projects are known to use pylint to help develop better code:
Also notice that the CheeseCake kwalitee reporting tool uses pylint to analyze the source code.
pylint expects the name of a package or module as argument. As a convenience, you can give to it a file name if it's possible to guess a module name from the file's path, using the python path. Some examples :
"pylint mymodule.py" should always works 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.
"pylint /whatever/directory/mymodule.py" will work if either:
- "/whatever/directory" is in the python path
- your cwd is "/whatever/directory"
- "directory" is a python package and "/whatever" is in the python path
- "directory" is a python package and your cwd is "/whatever" and so on...
Yes. That's actually due to a bug in psyco, making the locals() function for objects inheriting from psyobj returning an empty dictionary. For the moment, the only way to fix this is to use the PYLINT_IMPORT environment variable to not use psyco during pylint checking. Sample code
import os
try:
if os.environ.has_key('PYLINT_IMPORT'):
raise ImportError()
from psyco.classes import psyobj
except ImportError:
class psyobj:
pass
NOTICE: this problem should not occurs with pylint >= 0.5 since from this version pylint is not looking anymore for information in living objects (i.e. it doesn't anymore import analysed modules)
Yes, you can disable or enable (globally disabled) message at the module level by adding the corresponding option in a comment at the top of the file:
# pylint: disable-msg=W0401, E0202 # pylint: enable-msg=C0302
Analysis data are stored as pickle file in a directory which is localized using the following rules:
You can always generate a sample pylintrc file with --generate-rcfile Every option present on the command line before this will be included in the rc file
For example:
pylint --disable-msg=W0702,C0103 --class-rgx='[A-Z][a-z]+' --generate-rcfile