How to use the formencode.validators function in FormEncode

def fields(self):
        fields = ew_core.NameList()
        fields.append(ffw.MarkdownEdit(name='text'))
        fields.append(ew.HiddenField(name='forum', if_missing=None))
        fields.append(ew.Checkbox(name='subscribe', label='Subscribe', if_missing=False))
        if ew_core.widget_context.widget:
            # we are being displayed
            if ew_core.widget_context.render_context.get('show_subject', self.show_subject):
                fields.append(
                    ew.TextField(name='subject', attrs=dict(style="width:97%")))
        else:
            # We are being validated
            validator = fev.UnicodeString(not_empty=True, if_missing='')
            fields.append(ew.TextField(name='subject', validator=validator))
            fields.append(NullValidator(name=self.att_name))
        return fields

    @expose('json')
    @validate(validators={'file_id': validators.Int(),
                          'budge_infront_id': validators.Int()})
    def reorder_file(self, id, file_id, budge_infront_id, **kwargs):
        """Change the position of the given file relative to the 2nd file.

        :param file_id: The file to move
        :type file_id: ``int``
        :param budge_infront_id: The file whos position the first file takes.
            All files behind/after this file are bumped back as well.
        :type budge_infront_id: ``int`` or ``None``
        :rtype: JSON dict
        :returns:
            success
                bool

        """
        media = fetch_row(Media, id)

class AuthorizationResponsePackageValidator(Schema):
    """Authorization Response Package entity validator"""
    service_pins = ForEach()
    auth_request = validators.String()  # UUID
    response = validators.Bool()
    device_id = validators.String()
    allow_extra_fields = True


class AuthMethodsValidator(Schema):
    """Auth methods validator"""
    method = validators.String()
    set = validators.Bool(if_empty=None)
    active = validators.Bool(if_empty=None)
    allowed = validators.Bool(if_empty=None)
    supported = validators.Bool(if_empty=None)
    user_required = validators.Bool(if_empty=None)
    passed = validators.Bool(if_empty=None)
    error = validators.Bool(if_empty=None)


class GeoFenceValidator(Schema):
    """ GeoFence Validator, can represent both GeoFence and GeoCircleFence """
    name = validators.String(if_missing=None)
    latitude = validators.Number()
    longitude = validators.Number()
    radius = validators.Number()


class GeoCircleFenceValidator(GeoFenceValidator):
    """ GeoFence Validator, can represent ONLY GeoCircleFence """
    type = validators.OneOf(["GEO_CIRCLE"])

name = validators.UnicodeString(not_empty=True)


class NoteSchema(Schema):
    allow_extra_fields = True

    name = validators.UnicodeString(not_empty=True)
    text = validators.UnicodeString(not_empty=True)
    pad_id = validators.Int()


class ForgotPasswordSchema(Schema):
    allow_extra_fields = False

    email = All(EmailExists(), validators.Email(not_empty=True))


class ChangePasswordSchema(Schema):
    allow_extra_fields = False

    old_password = All(PasswordCorrect(), validators.UnicodeString(min=6))
    password = validators.UnicodeString(min=6)
    confirm_password = validators.UnicodeString(min=6)
    passwords_match = [
        validators.FieldsMatch('password', 'confirm_password')
    ]

""" need a special class that will allow None through but not '' """
    def is_empty(self, value):
        # only consider None empty, not an empty string
        return value is None


class _ValidatesMinLength(ValidatorBase):
    fe_validator = _MinLength

    def arg_for_fe_validator(self, index, unknown_arg):
        if isinstance(unknown_arg, int):
            return True
        return False


class _IPAddress(fev.IPAddress):
    """ need a special class that will allow None through but not '' """
    def is_empty(self, value):
        # only consider None empty, not an empty string
        return value is None


class _ValidatesIPAddress(ValidatorBase):
    fe_validator = _IPAddress


class _URL(fev.URL):
    """ need a special class that will allow None through but not '' """
    def is_empty(self, value):
        # only consider None empty, not an empty string
        return value is None

allow_extra_fields = True
    filter_extra_fields = True

    name = formencode.validators.String(if_missing=None)
    description = formencode.validators.String(if_missing=None)

    os_variant = formencode.validators.String(if_missing=None)
    os_type = formencode.validators.String(if_missing=None)
    os_arch = formencode.validators.String(if_missing=None)
    hypervisor = formencode.validators.String(if_missing=None)
    owner = formencode.validators.String(if_missing=None)

    expires = formencode.validators.String(if_missing=None)

    #expires = formencode.validators.DateTime???
    read_only = formencode.validators.StringBool(if_missing=None)
    unauthenticated_access = formencode.validators.StringBool(if_missing=None)

def validate_raw_image(params):
    schema = NewImageForm()
    try:
        result = schema.to_python(params)
    except formencode.validators.Invalid, error:
        for e,v in error.error_dict.iteritems():
            if e=='name' and v.state=='CONFLICT':
                abort(409, '409 Conflict')
            else:
                abort(400, '400 Bad Request')
    else:
        return result

class RawImageForm(formencode.Schema):

for plugin in getFactoredPlugins():
        pluginpath = os.path.join(app.base_auth_url, plugin.path)
        if pluginpath == req.path:
            return plugin(req)


class UsernameSchema(BaseSchema):
    username = validators.MinLength(3, not_empty=True)
    referrer = validators.UnicodeString(if_missing=u'')


class CodeSchema(BaseSchema):
    username = validators.MinLength(3, not_empty=True)
    code = validators.MinLength(4, not_empty=True)
    remember = validators.Bool()
    referrer = validators.UnicodeString(if_missing=u'')


class BasePlugin(object):
    name = None
    path = None
    username_schema = UsernameSchema
    code_schema = CodeSchema
    content_renderer = "templates/auth.pt"

    _formtext = {
        'title': None,
        'legend': None,
        'username': {
            'label': None,
            'desc': None
        },

email = validators.Email(not_empty=True)
    password = validators.UnicodeString(min=6)


class PadSchema(Schema):
    allow_extra_fields = True

    name = validators.UnicodeString(not_empty=True)


class NoteSchema(Schema):
    allow_extra_fields = True

    name = validators.UnicodeString(not_empty=True)
    text = validators.UnicodeString(not_empty=True)
    pad_id = validators.Int()


class ForgotPasswordSchema(Schema):
    allow_extra_fields = False

    email = All(EmailExists(), validators.Email(not_empty=True))


class ChangePasswordSchema(Schema):
    allow_extra_fields = False

    old_password = All(PasswordCorrect(), validators.UnicodeString(min=6))
    password = validators.UnicodeString(min=6)
    confirm_password = validators.UnicodeString(min=6)
    passwords_match = [
        validators.FieldsMatch('password', 'confirm_password')

    @without_trailing_slash
    @expose()
    @validate(dict(
            since=h.DateTimeConverter(if_empty=None, if_invalid=None),
            until=h.DateTimeConverter(if_empty=None, if_invalid=None),
            page=validators.Int(if_empty=None),
            limit=validators.Int(if_empty=None)))
    def feed(self, since=None, until=None, page=None, limit=None):
        if request.environ['PATH_INFO'].endswith('.atom'):
            feed_type = 'atom'
        else:
            feed_type = 'rss'
        title = 'Recent changes to Project %s' % c.project.name
        feed = M.Feed.feed(
            dict(project_id=c.project._id),
            feed_type,
            title,
            c.project.url(),
            title,
            since, until, page, limit)
        response.headers['Content-Type'] = ''
        response.content_type = 'application/xml'