monkey_patch_dataclass_init.py

def mapInitArgs(cls, fromType, toType, translateFun):
    oldinit = cls.__init__
    def newinit(self, *args, **kwargs):
        fields = cls.__dataclass_fields__
        fieldIter = iter(fields)
        for pos,arg in enumerate(args):
            fieldName = next(fieldIter)
            if fields[fieldName].type is toType and type(arg) is fromType:
                args[pos] = translateFun(arg)
        for fieldName in fieldIter:
            if fields[fieldName].type is toType and fieldName in kwargs:
                kwarg = kwargs[fieldName]
                if type(kwarg) is fromType:
                    kwargs[fieldName] = translateFun(kwarg)
        return oldinit(self, *args, **kwargs)
    cls.__init__ = newinit

mapInitArgs(SchoolTerm, str, datetime.datetime, dateutil.parser)