class RegisterForm(Form):
         username = StringField('Username', validators=[Required()])
         password = PasswordField('Password', validators=[Required(), EqualTo('password2',
 message='Passwords must match.')])
         password2 = PasswordField('Confirm Password', validators=[Required()])
         submit = SubmitField('Register')

         def validate_username(self, field):
             if User.query.filter_by(username=field.data).first():
                 raise ValidationError('Username already in use.')