python - flask 路线与引导模式形式不能很好地配合，生成形式未定义的错误

Question

当测试页面的“登录失败”错误消息部分时，我不断收到表单未定义的 jinja 错误。我对使用 Python/Flask 进行编码以及使用引导模式和表单非常陌生，所以我确信我忽略的东西很简单。因为我使用的是模态，所以我需要将命令添加到 python 代码中的每个页面路由，我觉得错误出在我在那里使用的嵌套 If 中。

我尝试移动 Flask 代码，以便首先运行登录部分，但无论我尝试什么，我都会遇到相同的错误。我可以使用已知的、良好的用户名/密码登录，并且可以毫无问题地注册新用户名。如果信息太多，我深表歉意，我以前没有在这里发布过，但我经常使用它来进行故障排除，所以我有很好的感觉这里的社区可以发现我做错了什么。

这是Python

#Define routes
@app.route('/home', methods=['GET', 'POST'])
def index():
    #Allow registry from page
    form = RegisterForm(request.form)
    if request.method == 'POST' and form.validate():
        name = form.name.data
        email = form.email.data
        username = form.username.data
        password = sha256_crypt.encrypt(str(form.password.data))

        # Execute query
        engine.execute("INSERT INTO users(name, email, username, password) VALUES(?, ?, ?, ?)", (name, email, username, password))
        # Changes Auto Commit so there is no need for opening a session or running a commit line.

        flash('You are now registered and can log in', 'success')

        return redirect(url_for('index'))
    else:
         #Allow login from page
        if request.method == 'POST':
            # Get Form Fields
            username = request.form['username']
            password_candidate = request.form['password']
            # Get user by username
            result = engine.execute("SELECT Username, Password FROM users WHERE username = ?", [username])

            # Get stored hash
            data = result.fetchone()
            if data is None:
                error = 'Username not found'
                return render_template('home.html', error=error)

            password = data['Password']

            # Compare Passwords
            if sha256_crypt.verify(password_candidate, password):
                # Passed
                session['logged_in'] = True
                session['username'] = username

                flash('You are now logged in', 'success')

                return redirect(url_for('dashboard'))
            else:
                error = 'Invalid login'
            return render_template('home.html', error=error)
    return render_template('home.html', form=form)

这是 HTML

<nav class="navbar navbar-expand-lg navbar-dark bg-dark">
    <a class="navbar-brand" href="#"><img src="/static/images/kissclipart-sti-logo2.png"></a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
    {% if session.logged_in %}
    <div class="collapse navbar-collapse" id="navbarSupportedContent">
      <ul class="navbar-nav mr-auto">
        <li class="nav-item">
          <a class="nav-link" href="/home"><i class="fas fa-home"></i> Home <span class="sr-only">(current)</span></a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="/about"><i class="fas fa-chalkboard"></i> About Us</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="/articles"><i class="fas fa-book"></i> Articles</a>
        </li>
        <li class="nav-item dropdown">
          <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
            Dropdown
          </a>
          <div class="dropdown-menu" aria-labelledby="navbarDropdown">
            <a class="dropdown-item" href="#">Action</a>
            <a class="dropdown-item" href="#">Another action</a>
            <div class="dropdown-divider"></div>
            <a class="dropdown-item" href="#">Something else here</a>
          </div>
        </li>
      </ul>
      {% else %}
      <div class="collapse navbar-collapse" id="navbarSupportedContent">
          <ul class="navbar-nav mr-auto">
            <li class="nav-item">
              <a class="nav-link" href="/home"><i class="fas fa-home"></i> Home <span class="sr-only">(current)</span></a>
            </li>
            <li class="nav-item">
              <a class="nav-link" href="/about"><i class="fas fa-chalkboard"></i> About Us</a>
            </li>
          </ul>
      {% endif %}
      <ul class="navbar-nav navbar-right">
      {% if session.logged_in %}
      <li class="nav-item">
     <!--   <button type="button" class="btn btn-secondary" onclick="window.location.href='/dashboard'"><i class="fas fa-tachometer-alt"></i> Dashboard</a></li> -->
          <a class="nav-link" href="/dashboard"><i class="fas fa-tachometer-alt"></i> Dashboard </a>
      <li class="nav-item">
      <!-- LogOut Modal Button -->
  <!-- <button type="button" class="btn btn-primary" data-toggle="modal" data-target="#Logout_Modal"><i class="fas fa-sign-out-alt"></i> 
        Log out
      </button> -->
      <a class="nav-link" data-toggle="modal" data-target="#Logout_Modal" href="#Logout_Modal"><i class="fas fa-sign-out-alt"></i> Logout </a>
      <!-- Modal -->
      <div class="modal fade" id="Logout_Modal" tabindex="-1" role="dialog" aria-labelledby="Logout_ModalLabel" aria-hidden="true">
        <div class="modal-dialog" role="document">
          <div class="modal-content">
            <div class="modal-header">
              <h5 class="modal-title" id="Logout_ModalLabel">Log out?</h5>
              <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                <span aria-hidden="true">&times;</span>
              </button>
            </div>
            <div class="modal-body">
              Are you sure you want to logout?
            </div>
            <div class="modal-footer">
              <button type="button" class="btn btn-outline-danger" data-dismiss="modal">No, still working!</button>
              <button type="button" class="btn btn-outline-success" onclick="window.location.href='/logout';">Yup, all done!</button>
            </div>
          </div>
        </div>
      </div>
    </ul>
    <form class="form-inline my-2 my-lg-0">
      <input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">
      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
    </form>
  </div>
</nav>
        {% else %}
        <li class="nav-item mr-auto">
        <!-- Register Modal Button -->
        <button type="button" class="btn btn-outline-success" data-toggle="modal" data-target="#Register_Modal"><i class="fas fa-user-plus"></i>
            Register?
          </button>
          <!-- Modal -->
          <div class="modal fade" id="Register_Modal" role="dialog" aria-labelledby="Register_ModalLabel" aria-hidden="true">
            <div class="modal-dialog" role="document">
              <div class="modal-content">
                <div class="modal-header">
                  <h5 class="modal-title" id="Register_ModalLabel">Let's get registered!</h5>
                  <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                  </button>
                </div>
                <div class="modal-body">
                    <h1>Register</h1>
                    {% from "includes/_formhelpers.html" import render_field %}
                    <form method="POST" action="">
                      <div class="form-group">
                        {{render_field(form.name, class_="form-control")}}
                      </div>
                      <div class="form-group">
                        {{render_field(form.email, class_="form-control")}}
                      </div>
                      <div class="form-group">
                        {{render_field(form.username, class_="form-control")}}
                      </div>
                      <div class="form-group">
                        {{render_field(form.password, class_="form-control")}}
                        <p>Your Password is required to be 6 characters long, a strong password is suggested. Please see the example below</p>
                        <p>Ex: Th1s1s@cceptabl3!</p>
                      </div>
                      <div class="form-group">
                        {{render_field(form.confirm, class_="form-control")}}
                      </div>
                      <p><input type="submit" class="btn btn-outline-success" value="Submit"></p>
                      <button type="button" class="btn btn-outline-danger" data-dismiss="modal">No, I changed my mind!</button>
                    </form>
                </div>
                <div class="modal-footer justify-content-between">
                    <div mr-auto> Already a member? <a href="#" data-toggle="modal" data-target="#Login_Modal" data-dismiss="modal">  Sign in here!</a></div>
              </div>
            </div>
          </div>

        <li class="nav-item mr-auto">
          <!-- Login Modal Button -->
          <button type="button" class="btn btn-outline-light" data-toggle="modal" data-target="#Login_Modal"><i class="fas fa-sign-in-alt"></i> 
            Login
            </button>
            <!-- Modal -->
            <div class="modal fade" id="Login_Modal"  role="dialog" aria-labelledby="Login_ModalLabel" aria-hidden="true">
              <div class="modal-dialog" role="document">
                <div class="modal-content">
                  <div class="modal-header">
                    <h5 class="modal-title" id="Login_ModalLabel">Ready to log in?</h5>
                    <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                      <span aria-hidden="true">&times;</span>
                    </button>
                  </div>
                  <div class="modal-body">
                      <form action="" method="POST">
                          <div class="form-group">
                            <label>Username</label>
                            <input type="text" name="username" required placeholder="JSmith" autofocus="autofocus" class="form-control" value={{request.form.username}}>
                          </div>
                          <div class="form-group">
                            <label>Password</label>
                            <input type="password" name="password" required class="form-control" value={{request.form.password}}>
                          </div>
                          <button type="submit" class="btn btn-outline-success">Login!</button>
                          <button type="button" class="btn btn-outline-danger" data-dismiss="modal">Not right now</button>
                        </form>
                  </div>
                  <div class="modal-footer justify-content-between">
                    <div mr-auto> Not a member? <a href="#" data-toggle="modal" data-target="#Register_Modal" data-dismiss="modal">  Sign up here!</a></div>
                  </div>
                </div>
              </div>
            </div>
          </li>
      {% endif %}
    </ul>
  </div>
</nav>

这是我得到的错误:

jinja2.exceptions.UndefinedError
jinja2.exceptions.UndefinedError: 'form' is undefined

Traceback (most recent call last)
File "C:\ProgramData\CooperConda\lib\site-packages\flask\app.py", line 2463, in __call__
return self.wsgi_app(environ, start_response)
File "C:\ProgramData\CooperConda\lib\site-packages\flask\app.py", line 2449, in wsgi_app
response = self.handle_exception(e)
File "C:\ProgramData\CooperConda\lib\site-packages\flask\app.py", line 1866, in handle_exception
reraise(exc_type, exc_value, tb)
File "C:\ProgramData\CooperConda\lib\site-packages\flask\_compat.py", line 39, in reraise
raise value
File "C:\ProgramData\CooperConda\lib\site-packages\flask\app.py", line 2446, in wsgi_app
response = self.full_dispatch_request()
File "C:\ProgramData\CooperConda\lib\site-packages\flask\app.py", line 1951, in full_dispatch_request
rv = self.handle_user_exception(e)
File "C:\ProgramData\CooperConda\lib\site-packages\flask\app.py", line 1820, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "C:\ProgramData\CooperConda\lib\site-packages\flask\_compat.py", line 39, in reraise
raise value
File "C:\ProgramData\CooperConda\lib\site-packages\flask\app.py", line 1949, in full_dispatch_request
rv = self.dispatch_request()
File "C:\ProgramData\CooperConda\lib\site-packages\flask\app.py", line 1935, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "C:\Users\tlquickl\devel\MyFlaskApp\app.py", line 61, in index
return render_template('home.html', error=error)
File "C:\ProgramData\CooperConda\lib\site-packages\flask\templating.py", line 140, in render_template
ctx.app,
File "C:\ProgramData\CooperConda\lib\site-packages\flask\templating.py", line 120, in _render
rv = template.render(context)
File "C:\ProgramData\CooperConda\lib\site-packages\jinja2\asyncsupport.py", line 76, in render
return original_render(self, *args, **kwargs)
File "C:\ProgramData\CooperConda\lib\site-packages\jinja2\environment.py", line 1008, in render
return self.environment.handle_exception(exc_info, True)
File "C:\ProgramData\CooperConda\lib\site-packages\jinja2\environment.py", line 780, in handle_exception
reraise(exc_type, exc_value, tb)
File "C:\ProgramData\CooperConda\lib\site-packages\jinja2\_compat.py", line 37, in reraise
raise value.with_traceback(tb)
File "C:\Users\tlquickl\devel\MyFlaskApp\templates\home.html", line 1, in top-level template code
{% extends 'layout.html' %}

{% block body %}
  <div class="center">
    <div class="jumbotron text-center">
        <h1>Welcome to My FlaskApp</h1>
File "C:\Users\tlquickl\devel\MyFlaskApp\templates\layout.html", line 23, in top-level template code

    <script type="text/javascript">
        CKEDITOR.replace('editor')
    </script>

    {% include 'includes/_navbar.html' %}
    <div class="container">
        {% include 'includes/_messages.html' %}
        {% block body %}{% endblock %}
    </div>
<script>
File "C:\Users\tlquickl\devel\MyFlaskApp\templates\includes\_navbar.html", line 100, in top-level template code
                <div class="modal-body">
                    <h1>Register</h1>
                    {% from "includes/_formhelpers.html" import render_field %}
                    <form method="POST" action="">
                      <div class="form-group">
                        {{render_field(form.name, class_="form-control")}}
                      </div>
                      <div class="form-group">
                        {{render_field(form.email, class_="form-control")}}
                      </div>
                      <div class="form-group">
File "C:\ProgramData\CooperConda\lib\site-packages\jinja2\environment.py", line 430, in getattr
return getattr(obj, attribute)
jinja2.exceptions.UndefinedError: 'form' is undefined
The debugger caught an exception in your WSGI application. You can now look at the traceback which led to the error.
To switch between the interactive traceback and the plaintext one, you can click on the "Traceback" headline. From the text traceback you can also create a paste of it. For code execution mouse-over the frame you want to debug and click on the console icon on the right side.

You can execute arbitrary Python code in the stack frames and there are some extra helpers available for introspection:

dump() shows all variables in the frame
dump(obj) dumps all that's known about the object
Brought to you by DON'T PANIC, your friendly Werkzeug powered traceback interpreter.

我希望收到错误消息并返回主页，但我收到了包含的错误。我正在使用 Flask、SQLAlchemy 和 WTForms。

非常感谢任何帮助!

Answer 1

非常感谢 NemoMeMeliorEst!

我将代码更改为以下内容，现在它可以工作了! (减去**，添加那些是为了强调改变)

 # Get stored hash
            data = result.fetchone()
            if data is None:
                error = 'Username not found'
                return render_template('home.html', error=error, ***form=form***)
            password = data['Password']
            # Compare Passwords
            if sha256_crypt.verify(password_candidate, password):
                # Passed
                session['logged_in'] = True
                session['username'] = username
                flash('You are now logged in', 'success')
                return redirect(url_for('dashboard'))
            else:
                error = 'Invalid login'
            return render_template('home.html', error=error, ***form=form***)
    return render_template('home.html', form=form)