fwiw sqlalchemy also allow validators to change the value: https://docs.sqlalchemy.org/en/20/orm/mapped_attributes.html#simple-validators

A quick way to add a “validation” routine to an attribute is to use the validates() decorator. An attribute validator can raise an exception, halting the process of mutating the attribute’s value, or can change the given value into something different.

i agree it isn't immediately apparent given the name "validators", but perhaps that's preferable than to adding more API surface? i'm not sure yet.

Are we trying to implement pre/post - load/dump but at field level rather than schema level? Should we do that instead?

that's an interesting idea. something like

class ArtistSchema(Schema):
    name = fields.Str(post_load=(strip_whitespace, uppercase))
    email = fields.Str(post_load=(strip_whitespace, uppercase))

# and/or

class ArtistSchema(Schema):
    name = fields.Str()
    email = fields.Str()

    @field_post_load("name", "email")
    def strip_whitespace(self, field_name: str, value: str) -> str:
        return value.strip()

i like this idea, but will have to give it some thought

i suppose one downside of that would be that validate/validates becomes somewhat redundant with post_load/field_post_load, right?

otoh, it's nice that field_pre/post_load/dump could be added as a non-breaking feature

i suppose one downside of that would be that validate/validates becomes somewhat redundant with post_load/field_post_load, right?

Possibly. But the call is not exactly the same since validate expects a validator, not a function.