Create a customer converter and validator using ATTRS

I am trying to learn attrs and I have two questions. Please note that I am using the ATTRS library, not ATTR.

1. How do I create a converter to change typ to uppercase? —> I solved this question. The formula below is updated. :)
2. How do I create a validator to ensure that typ is contained within a list?

I’ve tried many things on both, but to no avail. The documentation does not show how to make either a custom converter or validator- or, at least, I do not understand if it does.

from attrs import define, field, validators, setters
from datetime import datetime

@define(slots=True)
class Trans:
    acct:   int     = field(validator=validators.instance_of(int), converter=int)
    id:     int     = field(validator=validators.instance_of(int), converter=int)
    ts:     datetime= field(validator=validators.instance_of(datetime))
    typ:    str     = field(converter=(lambda x: x.upper()))

@typ.validator   # this does not work
def typCheck(self, attrib, val):
    if val not in ['A','B','W']:
        raise ValueError('Must be one of these options: ' + str(typs))

a = Trans(1,1,utc,'w')

Thank you in advance!

Answer

For whomever needs it, here is the answer.

from attrs import define, field, validators, setters
from datetime import datetime

typs = ['O', 'D', 'W', 'C']

@define(slots=True)
class Trans:
    acct:   int     = field(validator=validators.instance_of(int), converter=int)
    id:     int     = field(validator=validators.instance_of(int), converter=int)
    ts:     datetime= field(validator=validators.instance_of(datetime))
    typ:    str     = field(converter=(lambda x: x.upper()))

    @typ.validator
    def typCheck(self, attrib, val):
        if val not in typs:
            raise ValueError('Must be one of these options: ' + str(typs))

a = Trans(1,1,utc,'w')
a