为什么在Python Flask中没有显示登录错误消息

from flask import flash

app.secret_key = 'your_secret_key'

from flask import flash

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        # 验证登录信息
        if login_success:
            # 登录成功
            return redirect(url_for('home'))
        else:
            flash('登录失败，请检查用户名和密码')
            return redirect(url_for('login'))
    return render_template('login.html')

{% with messages = get_flashed_messages() %}
  {% if messages %}
    <ul class="flashes">
      {% for message in messages %}
        <li>{{ message }}</li>
      {% endfor %}
    </ul>
  {% endif %}
{% endwith %}

from flask import flash, redirect, url_for

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        # 验证登录信息
        if login_success:
            # 登录成功
            return redirect(url_for('home'))
        else:
            flash('登录失败，请检查用户名和密码')
            return redirect(url_for('login'))
    return render_template('login.html')