def validate(self): if request.form["user_name"] is None or request.form["user_name"].strip()=="": return False inserted_username = request.form["user_name"] user = Users.query.filter_by(user_name = inserted_username).first() if user != None: suggested_username = Users.create_unique_username(inserted_username) flash('This username already exists. Consider register with %s' % suggested_username) return False return True