def validate(self, **kw):
        params = dict(username=kw['username'], email=kw['email'])
        if (self.valid_username(kw['username'], params) and
            self.valid_email(kw['email'], params) and
            self.valid_password(kw['password'], kw['verify'], params)):
           return True, params
        else:
           return False, params

    def valid_username(self, username, params):
        if username and re.match(r"^[a-zA-Z0-9_-]{3,20}$", username):
            return True
        else:
            params['error_username'] = "username is wrong"

    def valid_password(self, password, verify, params):
        if password and re.match(r"^.{3,20}$", password):
            if not (password == verify):
                params['error_verify'] = "passwords should be the same"
                return
            return True
        else:
            params['error_password'] = "password is wrong"

    def valid_email(self, email, params):
        if not email or re.match(r'^[\S]+@[\S]+\.[\S]+$', email):
            return True
        else:
            params['error_email'] = "that's not a valid email"