Flask返回TypeError：视图函数未返回有效响应

Question

I am new to Flask and trying to build simple userform page using flask and running into error. When I am trying to render just pure HTML, extending base.html, everything works perfectly, however when added macro, result is below. I tried everything and cannot solve the issue on my own. Any hints, what am I doing wrong?

[2019-07-09 22:19:39,837] ERROR in app: Exception on / [GET]
Traceback (most recent call last):
  File "path/venv/lib/python3.6/site-packages/flask/app.py", line 2446, in wsgi_app
    response = self.full_dispatch_request()
  File "path/venv/lib/python3.6/site-packages/flask/app.py", line 1952, in full_dispatch_request
    return self.finalize_request(rv)
  File "path/venv/lib/python3.6/site-packages/flask/app.py", line 1967, in finalize_request
    response = self.make_response(rv)
  File "path/venv/lib/python3.6/site-packages/flask/app.py", line 2130, in make_response
    " {rv.__class__.__name__}.".format(rv=rv)
TypeError: The view function did not return a valid response. The return type must be a string, dict, tuple, Response instance, or WSGI callable, but it was a UserForm.
127.0.0.1 - - [09/Jul/2019 22:19:39] "GET / HTTP/1.1" 500 -

This is my Python code:

from app import app
from flask import render_template
from flask_wtf import FlaskForm
from wtforms import StringField, TextAreaField, SelectField
from wtforms.validators import InputRequired


@app.route('/', methods=['GET', 'POST'])

class UserForm(FlaskForm):
    prefix = StringField("Prefix", validators=[InputRequired()])
    anrede = StringField("Anrede", validators=[InputRequired()])

def form():
    form = UserForm()
    return render_template('html_one_flask.html', form=form)

form which I am trying to load

{% extends "base.html" %}

{% from "render_field.html" import render_field %}
{% block content %}

<div class = "container">
    <div class = "spacer" > </div>
</div>
<div class = "container" id = "data_category">PERSONAL DATEN</div>
<div class = "container">
    <div class = "spacer" > </div>
        <div class="form-group row flex-v-center" id = 1>
            {{ render_field(form.prefix), placeholder = form.prefix.label.text }}
            {{ render_field(form.anrede), placeholder = form.anrede.label.text }}
        </div>
</div>
{% endblock %}

and macro imported from another file

{% macro render_field(field) %}

<div class = "col-0.75">
    <div class = "spacer_label" > </div>
    <label for="{{ field.name }}">{{ field.label.text }} </label>
</div>
<div class = "col-1">
    {{ field(class_ = "form-control input-sm", **kwargs|safe }}
</div>

{% endmacro %}

Answer 1

Your @app.route should be above the view function, not the class declaration:

@app.route('/', methods=['GET', 'POST'])
def form():
    ...

Answer 2

您将@ app.route装饰器放在了黄色的地方