Custom Field Validation and Cleaning

We have seen how a Django form converts values from an HTTP request, which are strings, into Python objects. In a non-custom Django form, the target type is dependent on the field class. For example, the Python type derived from IntegerField is int, and string values are given to us verbatim, as the user entered them. But we can also implement methods on our Form class to alter the output values from our fields in any way we choose. The allows us to clean or filter the user's input data to fit what we expect better. We could round an integer to the nearest multiple of ten to fit into a batch size for ordering specific items. Or we could transform an email address to lowercase so that the data is consistent for searching.

We can also implement some custom validators. We will look at a couple of different ways of validating fields: by writing a custom validator, and by writing a custom clean method for the field. Each method has its pros and...