表单验证，以显示表单用户在哪个字段中输入了重复数据

Question

def add_users():
    if request.method == "POST":
        username = request.form['username']
        password = request.form['password']  
        email = request.form['email']
        site_url = request.form['site_url']
        user = User.query.get(username)
        print user
        usr = User.query.get(email)
        print usr
        use = User.query.get(site_url)
        print use
         if user:
             flash('Duplicate Username detected')
         if usr:
             flash('Duplicate Email detected')
         if use:
             flash('Duplicate URL site detected')
        try:
            site = User(username,password,email,site_url,'')
            db.session.add(site)
            db.session.commit()
            flash('User Successfully added')
        except TypeError:
            pass
        except IntegrityError:
            db.session.rollback()
            flash('Duplicate entry detected')
    return render_template("add_users.html")

我已经编写了一个python代码来在数据库中添加用户。它将检测是否检测到重复数据，并回滚数据库。假设，如果我想知道用户在字段的哪种形式中输入了重复数据。此代码无法从表单中获取数据，无法与现有用户一起查询表单。当我打印试图获取表单字段数据的字段时，它将显示“无”。无法从表单中获取数据。我希望能够显示用户在表单的哪个字段中输入了重复数据，并显示您在该字段中输入了重复数据。有人能帮我吗？ 任何帮助都将不胜感激。 多谢各位

这是我的HTML代码

<div class= "content" style="z-index: 1">
    <div class="row">
        <div class="wrapper col-md-offset-4 col-md-4 col-md-offset-4">
            <form action="/auth/add_users" method="post" name="Add_Form">       
                <h3 class="text-center">Add User</h3>
                <hr>
                <div class="form-group">
                    <h4> Username </h4>
                    <input type="text" class="form-control Email/Username" name="username" id="username" placeholder="username" required="true" autofocus="" />
                </div>
                <div class="form-group">
                    <h4> Password </h4>
                    <input type="password" class="form-control Password" name="password" id="password" placeholder="password" required="true"/>            
                </div>
                <div class="form-group">
                    <h4> Email </h4>
                    <input type="email" class="form-control Email/Username" name="email" id="email" placeholder="email" required="true" autofocus="" />
                </div>
                <div class="form-group">
                    <h4> Site_url </h4>
                    <input type="text" class="form-control site_url" name="site_url" id="site_url" placeholder="site_url" required="true" autofocus="" />
                </div>
                <div class="buttonalign">
                    <button class="btn btn-sm btn-primary btn-block" name="Submit" value="Submit" type="Submit" id="submit">Submit</button>
                </div>  
            </form>
        </div> 
    </div>
</div>