Pylint Quickstart
Author: Logilab
Keywords: logilab

| Pylint Quickstart

| Pylint Quickstart 1. Contents Link or reference ("what-is-pylint") to an inexistant target. What is pylint? Link or reference ("invoking-pylint") to an inexistant target. Invoking pylint Link or reference ("pylint-output") to an inexistant target. Pylint output Link or reference ("source-code-analysis-section") to an inexistant target. Source code analysis section Link or reference ("reports-section") to an inexistant target. Reports section Link or reference ("command-line-options") to an inexistant target. Command line options Link or reference ("bug-reports") to an inexistant target. Bug reports This document is meant to get you started with Pylint. It assumes that you have installed pylint following the instructions in the README document found in the source documentation. 2. 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 explicitly does not bother with coding style. The default coding style used by pylint is close to Guido's style guide. For more information about code smells, refer to Martin Fowler's refactoring book Pylint will display a number of errors and warnings as it analyzes the code, as well as some statistics about the number of warnings and errors found in different files. 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. 3. 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 restrictions. 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 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. For more details on this see the FAQ. 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. 4. 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. 4.1. 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) 4.2. 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). 5. Command line options First of all, we have two basic (but useful) options.
Option | Description
--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:
Option | Description
--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.
6. Bug reports 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. This mailing list is also a nice place to discuss Pylint issues.