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`from flask import Flask, render_template
    from flask_wtf import FlaskForm
    from wtforms import StringField, PasswordField, BooleanField
    from wtforms.validators import InputRequired, Email, length, ValidationError

    app = Flask(__name__)
    app.config['SECRET_KEY'] = 'This is a secret'
    class LoginForm(FlaskForm):
      username = StringField('username', validators=[InputRequired()])
      password = PasswordField('password')

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


    if __name__== '__main__':
      app.run(debug=True)

<html>
<title> MY FORM </title>
<body>
<form method="POST" action="{{ url_for('form') }}">
  {{form.csrf_token}}
  {{ form.username.label }}
  {{ form.username }}
  <ul>
  {% for error in form.username.errors %}
    <li style="color: red;">{{ error }} </li>

  {% endfor %}
  </ul>
  {{ form.password }}
  {{ form.password.label }}
  <input type="submit" value="Submit">

</form>
</body>
</html>