Proposal: Add `default`-normalization rule

[funkyfuture]

this is a follow-up of this.

A default-rule would substitute any None-values, empty Mapping and Sequence-instances and numbers equal to zero for a given field with the provided constraint's value while a document is normalized. if the field isn't present at all, it will be added to the document with the constraint's value.

the default-constraint should be processed after coercing.

example:

>>> schema = {'amount': {'default': 1}}
>>> document = {'amount': None}
>>> v.validated(document, schema)
{'amount': 1}
>>> document = {'model': 'The Robots'}
>>> v.normalized(document, schema)
{'model': 'The Robots', 'amount': 1}

[nicolaiarocci]

Now that we also transform the incoming document, I guess that stuff like this is welcome. Actually, we implemented a default rule in Eve so I know it is useful :) 👍

[funkyfuture]

Is there a difference of Eve's rule-design to my proposal?

[nicolaiarocci]

Yes. Of course Eve does not have or need normalized since input documents are stored to the backend (with defaults added as needed).