Frequently Asked Questions

1. About Pylint

1.1 What is Pylint?

Pylint is a static code checker, meaning it can analyse your code without actually running it. Pylint checks for errors, tries to enforce a coding standard, and tries to enforce a coding style.

2. Installation

2.1 How do I install Pylint?

Everything should be explained on http://pylint.readthedocs.io/en/latest/installation

2.2 What kind of versioning system does Pylint use?

Pylint uses the git distributed version control system. The URL of the repository is: https://github.com/PyCQA/pylint . To get the latest version of Pylint from the repository, simply invoke

git clone https://github.com/PyCQA/pylint

2.3 What are Pylint’s dependencies?

Pylint depends on astroid and a couple of other packages. It should be compatible with any Python version greater than 2.7.0 and it is also working on PyPy.

2.4 What versions of Python is Pylint supporting?

Since Pylint 1.4, we support only Python 2.7+ and Python 3.3+. If code uses new Python 3.6 syntax, minimal required version is Pylint 1.7.

Using this strategy really helps in maintaining a code base compatible with both versions and from this benefits not only the maintainers, but the end users as well, because it’s easier to add and test new features.

3. Running Pylint

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 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.

“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 an implicit namespace package and is in the python path.
  • “directory” is a python package and your cwd is “/whatever” and so on...

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 is localized 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-rcfile Every option present on the command line before this will be included in the 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. Read http://pylint.readthedocs.io/en/latest/ide-integration

4. Message Control

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 by adding “#pylint: disable=some-message,another-one” at the desired block level or 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 the module level by adding the corresponding option in a comment at the top 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 the module. Pylint 0.26.1 and up have renamed that directive to “#pylint: skip-file” (but the first version will be kept for backward compatibility).

In order to ease finding which modules are ignored an Information-level message file-ignored is emitted. With recent versions of Pylint, if you use the old syntax, an additional deprecated-disable-all message is emitted.

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 by cb_, as in cb_onclick(...). By doing so arguments usage won’t be checked. Another solution is to use one of the names defined in the “dummy-variables” configuration variable 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 configuration file. It means that if you need to disable a lot of messages, you can use tricks like:

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

4.7 Why are there a bunch of messages disabled by default?

pylint does have some messages disabled by default, either because they are prone to false positives or that they are opinionated enough for not being included as default messages. But most of the disabled messages are from the Python 3 porting checker, which is disabled by default. It needs special activation with the --py3k flag.

5. Classes and Inheritance

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 its methods 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 with a name which ends with “mixin” (whatever case).

6. Troubleshooting

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 no lower 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 negative values really bugs you, you can set the formula to be the maximum of 0 and the above expression.

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

Read http://pylint.readthedocs.io/en/latest/contribute#bug-reports-feedback

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

Read http://pylint.readthedocs.io/en/latest/contribute#mailing-lists