1.1 What is Pylint?¶

Pylint is astatic code checker, meaning it can analyse your code withoutactually running it. Pylint checks for errors, tries to enforce a codingstandard, and tries to enforce a coding style.

1.2 How is Pylint different from Pychecker?¶

A major difference between Pylint andPychecker is that Pylint checks forstyle issues, while Pychecker explicitly does not. There are a few otherdifferences, such as the fact that Pylint does not import live modules whilePychecker does (see6.2 Why does Pychecker catch problems with imports thatPylint doesn’t?).

1.3 Who wrote Pylint?¶

Pylint’s main author and maintainer for the first ten years of its life has beenSylvain Thénault, while he worked atLogilab where the project was born. For afull list of contributors, see the “Contributors” section of Pylint’s READMEfile.

1.4 Who uses Pylint?¶

Everybody knows someone who uses Pylint.

2.1 How do I install Pylint?¶

Everything should be explained onhttp://docs.pylint.org/installation

2.2 What kind of versioning system does Pylint use?¶

Pylint uses theMercurial distributed version control system. The URL of therepository is:https://bitbucket.org/logilab/pylint. To get the latest version ofPylint from the repository, simply invoke

hg clone https://bitbucket.org/logilab/pylint

2.3 What are Pylint’s dependencies?¶

Pylint requires the latestastroid. It should becompatible with any Python version greater than 2.7.0.

2.4 What versions of Python is Pylint supporting?¶

Since Pylint 1.4, we support only Python 2.7+ and Python 3.3+.Using this strategy really helps in maintaining a code base compatiblewith both versions and from this benefits not only the maintainers,but the end users as well, because it’s easier to add and testnew features.If support for Python 2.6 is absolutely required, then the versionfrom pylint-1.3 branch can be used. It will receive backports ofbug fixes for a while.

3.1 Can I give pylint a file as an argument instead of a module?¶

Pylint expects the name of a package or module as its argument. As aconvenience,you can give it a file name if it’s possible to guess a module name fromthe file’s path using the python path. Some examples :

“pylint mymodule.py” should always work since the current workingdirectory is automatically added on top of the python path

“pylint directory/mymodule.py” will work if “directory” is a pythonpackage (i.e. has an __init__.py file) or if “directory” is in thepython 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 pythonpath
• “directory” is a python package and your cwd is “/whatever” and soon...

3.2 Where is the persistent data stored to compare between successive runs?¶

Analysis data are stored as a pickle file in a directory which islocalized using the following rules:

• value of the PYLINTHOME environment variable if set

• ”.pylint.d” subdirectory of the user’s home directory if it is found

  (not always findable on Windows platforms)

• ”.pylint.d” directory in the current directory

3.3 How do I find the option name (for pylintrc) corresponding to a specific command line option?¶

You can always generate a sample pylintrc file with –generate-rcfileEvery option present on the command line before this will be included inthe rc file

For example:

pylint --disable=bare-except,invalid-name --class-rgx='[A-Z][a-z]+' --generate-rcfile

3.4 I’d rather not run Pylint from the command line. Can I integrate it with my editor?¶

Much probably. Readhttp://docs.pylint.org/ide-integration

4.1 Is it possible to locally disable a particular message?¶

Yes, this feature has been added in Pylint 0.11. This may be done byadding “#pylint: disable=some-message,another-one” at the desired block levelor at the end of the desired line of code

4.2 Is there a way to disable a message for a particular module only?¶

Yes, you can disable or enable (globally disabled) messages at themodule level by adding the corresponding option in a comment at thetop of the file:

# pylint: disable=wildcard-import, method-hidden# pylint: enable=too-many-lines

4.3 How can I tell Pylint to never check a given module?¶

With Pylint < 0.25, add “#pylint: disable-all” at the beginning of themodule. Pylint 0.26.1 and up have renamed that directive to“#pylint: skip-file” (but the first version will be kept for backwardcompatibility).

In order to ease finding which modules are ignored a Information-level messagefile-ignored is emited. With recent versions of Pylint, if you use the oldsyntax, an additionaldeprecated-disable-all message is emited.

4.4 Do I have to remember all these numbers?¶

No, starting from 0.25.3, you can use symbolic names for messages:

# pylint: disable=fixme, line-too-long

4.5 I have a callback function where I have no control over received arguments. How do I avoid getting unused argument warnings?¶

Prefix (ui) the callback’s name bycb_, as in cb_onclick(...). Bydoing so arguments usage won’t be checked. Another solution is touse one of the names defined in the “dummy-variables” configurationvariable for unused argument (“_” and “dummy” by default).

4.6 What is the format of the configuration file?¶

Pylint uses ConfigParser from the standard library to parse the configurationfile. It means that if you need to disable a lot of messages, you can usetricks like:

# disable wildcard-import, method-hidden and too-many-lines because I do# not want itdisable= wildcard-import, method-hidden, too-many-lines

5.1 When is Pylint considering a class as an abstract class?¶

A class is considered as an abstract class if at least one of itsmethods is doing nothing but raising NotImplementedError.

5.2 How do I avoid “access to undefined member” messages in my mixin classes?¶

To do so you have to set the ignore-mixin-members option to“yes” (this is the default value) and to name your mixin class witha name which ends with “mixin” (whatever case).

6.1 Pylint gave my code a negative rating out of ten. That can’t be right!¶

Even though the final rating Pylint renders is nominally out of ten, there’s nolower bound on it. By default, the formula to calculate score is

10.0-((float(5*error+warning+refactor+convention)/statement)*10)

However, this option can be changed in the Pylint rc file. If having negativevalues really bugs you, you can set the formula to be the maximum of 0 and theabove expression.

6.2 Why does Pychecker catch problems with imports that Pylint doesn’t?¶

Pychecker and Pylint use different approaches. pycheckerimports the modules and rummages around in the result, hence it sees mymangled sys.path. Pylint doesn’t import any of the candidate modules andthus doesn’t include any of import’s side effects (good and bad). Ittraverses an AST representation of the code.

6.3 Pylint keeps crashing withMaximum recursion depth exceeded¶

Pylint can crash with this error if you have a string in your analyzedprogram, created by joining a lot of strings with the addition operator.Due to how Pylint works, visiting nodes on a AST tree and due to howthe BinOp node is represented (the node which represents the string ‘1+1’for instance), the same visit method will be called over and over again, leadingto a maximum recursion error. You can alleviate this problem by passingthe flag–optimize-ast=y to Pylint. This will activate an optimizationwhich will transform such AST subtrees into the final resulting string.This flag is off by default. If this is not the case, please report a bug!

6.4 I think I found a bug in Pylint. What should I do?¶

Readhttp://docs.pylint.org/contribute#bug-reports-feedback

6.5 I have a question about Pylint that isn’t answered here.¶

Readhttp://docs.pylint.org/contribute#mailing-lists