Running Pylint#

On module packages or directories#

Pylint is meant to be called from the command line. The usage is

pylint [options] modules_or_packages

By default the pylint command only accepts a list of python modules and packages. On versions below 2.15, specifying a directory that is not an explicit package (with __init__.py) results in an error:

pylint mydir
************* Module mydir
mydir/__init__.py:1:0: F0010: error while code parsing: Unable to load file mydir/__init__.py:
[Errno 2] No such file or directory: 'mydir/__init__.py' (parse-error)

Thus, on versions before 2.15, or when dealing with certain edge cases that have not yet been solved, using the --recursive=y option allows for linting a namespace package:

pylint --recursive=y mydir mymodule mypackage

This option makes pylint attempt to discover all modules (files ending with .py extension) and all explicit packages (all directories containing a __init__.py file).

Pylint will not import this package or module, but it does use Python internals to locate them and as such is subject to the same rules and configuration. 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.

On files#

It is also possible to analyze Python files, with a few restrictions. As a convenience, you can give 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 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), an implicit namespace package or if directory is in the python path.

With implicit namespace packages#

If the analyzed sources use implicit namespace packages (PEP 420), the source root(s) should be specified using the --source-roots option. Otherwise, the package names are detected incorrectly, since implicit namespace packages don't contain an __init__.py.

Globbing support#

It is also possible to specify both directories and files using globbing patterns:

pylint [options] packages/*/src

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 architected around several checkers. You can disable a specific checker or some of its messages or message categories by specifying --disable=<symbol>. If you want to enable only some checkers or some message symbols, first use --disable=all then --enable=<symbol> with <symbol> being a comma-separated list of checker names and message symbols. See the list of available features for a description of provided checkers with their functionalities. The --disable and --enable options can be used with comma-separated lists mixing checkers, message ids and categories like -d C,W,no-error,design

It is possible to disable all messages with --disable=all. This is useful to enable only a few checkers or a few messages by first disabling everything, and then re-enabling only what you need.

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 configuration file to specify the default values. You can specify a configuration file on the command line using the --rcfile option. Otherwise, Pylint searches for a configuration file in the following order and uses the first one it finds:

  1. pylintrc in the current working directory

  2. .pylintrc in the current working directory

  3. pyproject.toml in the current working directory, providing it has at least one tool.pylint. section. The pyproject.toml must prepend section names with tool.pylint., for example [tool.pylint.'MESSAGES CONTROL']. They can also be passed in on the command line.

  4. setup.cfg in the current working directory, providing it has at least one pylint. section

  5. tox.ini in the current working directory, providing it has at least one pylint. section

  6. Pylint will search for the pyproject.toml file up the directories hierarchy unless it's found, or a .git/.hg directory is found, or the file system root is approached.

  7. If the current working directory is in a Python package, Pylint searches up the hierarchy of Python packages until it finds a pylintrc file. This allows you to specify coding standards on a module-by-module basis. Of course, a directory is judged to be a Python package if it contains an __init__.py file.

  8. The file named by environment variable PYLINTRC

  9. if you have a home directory which isn't /root:

    1. .pylintrc in your home directory

    2. .config/pylintrc in your home directory

  10. /etc/pylintrc

The --generate-toml-config option will generate a commented configuration file on standard output according to the current configuration and exit. This includes:

  • Any configuration file found as explained above

  • Options appearing before --generate-toml-config on the Pylint command line

Of course you can also start with the default values and hand-tune the configuration.

Other useful global options include:

--ignore=<file[,file...]>

Files or directories to be skipped. They should be base names, not paths.

--output-format=<format>

Select output format (text, json, custom).

--msg-template=<template>

Modify text output message template.

--list-msgs

Generate pylint's messages.

--list-msgs-enabled

Display a list of what messages are enabled and disabled with the given configuration.

--full-documentation

Generate pylint's full documentation, in reST format.

Parallel execution#

It is possible to speed up the execution of Pylint. If the running computer has more CPUs than one, then the work for checking all files could be spread across all cores via Pylints's sub-processes. This functionality is exposed via the -j command-line parameter. If the provided number is 0, then the total number of CPUs will be autodetected and used.

Example:

pylint -j 4 mymodule1.py mymodule2.py mymodule3.py mymodule4.py

This will spawn 4 parallel Pylint sub-process, where each provided module will be checked in parallel. Discovered problems by checkers are not displayed immediately. They are shown just after checking a module is complete.

There is one known limitation with running checks in parallel as currently implemented. Since the division of files into worker processes is indeterminate, checkers that depend on comparing multiple files (e.g. cyclic-import and duplicate-code) can produce indeterminate results.

Exit codes#

Pylint returns bit-encoded exit codes.

exit code

meaning

0

no error

1

fatal message issued

2

error message issued

4

warning message issued

8

refactor message issued

16

convention message issued

32

usage error

For example, an exit code of 20 means there was at least one warning message (4) and at least one convention message (16) and nothing else.