What is Pylint?

Pylint is a tool that checks for errors in Python code, tries to enforce a coding standard and looks for code smells. It can also look for certain type errors, it can recommend suggestions about how particular blocks can be refactored and can offer you details about the code’s complexity.

Other similar projects would include the now defunct pychecker, pyflakes, flake8 and mypy. The default coding style used by Pylint is close to PEP 008.

Pylint will display a number of messages as it analyzes the code and it can also be used for displaying 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.

Last but not least, the code is given an overall mark, based on the number and severity of the warnings and errors.

Pylint was born in 2003 at Logilab, that funded Sylvain Thénault to lead its development. Since 2015, the project went under the PyCQA umbrella, where it is currently maintained and developed by a couple of contributors.

What Pylint is not?

What Pylint says is not to be taken as gospel and Pylint isn’t smarter than you are: it may warn you about things that you have conscientiously done.

Pylint tries hard to report as few false positives as possible for errors, but it may be too verbose with warnings. That’s for example because it tries to detect things that may be dangerous in a context, but are 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 project!

The best way to tackle pylint’s verboseness is to:

  • enable or disable the messages or message categories that you want to be activated or not for when pylint is analyzing your code. This can be done easily through a command line flag. For instance, disabling all convention messages is simple as a --disable=C option added to pylint command.
  • create a custom configuration file, tailored to your needs. You can generate one using pylint’s command --generate-rcfile.
Quoting Alexandre Fayolle:

My usage pattern for Pylint is to generally run pylint -E quite often to get stupid errors flagged before launching an application (or before committing). 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:

  • stick to more naming conventions (unused variables ending in underscores, mix-in class names ending in “Mixin”)
  • making all abstract methods explicit (rather than just not defining them in the superclass)
  • add # pylint: disable=X0123 comments:
    • for messages which are useful in general, but not in a specific case
    • for Pylint bugs
    • for Pylint limitations (for instance Twisted’s modules create a lot of definitions dynamically so Pylint does not know about them)

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.