We all know we should "Automate the Boring Stuff™", but how often are you manually checking PRs against your internal style guide?

Django has a powerful inbuilt check framework which you're using every day... without even realising it.

Writing your own check

Once you've done the hard work of agreeing a coding standard with your team, next comes the fun bit... implementing the check.

In this example, I want an error to be raised if:

• a TextField or a CharField has blank=True null=True.
• any other field has set blank=True null=False.

To learn about why these are error states, see Demystifying nulls and blanks in Django.

To do this, I wrote a function to validate a field's properties and return an error, with a message and hint, when these are my error states.

I create and register my check run_model_field_checks which loops through all my model fields and collects a list of errors.

For this check to be picked up it, it must be in (or imported into) a file that’s loaded when your application is loaded. For example, in the AppConfig.ready() method.

Run the check

Checks are run by some management commands such as makemigrations and migrate.

You can also run checks directly with:

$ ./manage.py check

It's also a good idea to add this to your CI and to set the fail level:

$ ./manage.py check --fail-level=WARNING

Other check ideas

Here are a few more ideas:

• Raise a warning if a Field has no verbose_name.
• Raise an error if a verbose_name does not use gettext (if your project uses translations).
• Raise an error if the length of a choice option is greater than your max_length.