class LoginForm(FlaskForm):
    email = StringField('Email', validators=[Required(), Length(1, 64), Email()])
    password = PasswordField('Password', validators=[Required()])
    remember_me = BooleanField('Keep me logged in')
    submit = SubmitField('Login In')

 @auth.route('/login', methods=['GET', 'POST'])
def login():
    form = LoginForm()
    if form.validate_on_submit():
        user = User.query.filter_by(email=form.email.data).first()
        if user is not None and user.verify_password(form.password.data):
            login_user(user, form.remember_me.data)
            return redirect(request.args.get('next') or url_for('main.index'))
        flash('Invalid user name or password!!')
    return render_template('auth/login.html', form=form)

 {% macro render_field(field) %}
    <dt>{{ field.label }}
    <dd>{{ field(**kwargs)|safe }}
        {% if field.errors %}
            <ul class=errors>
                {% for error in field.errors %}
                    <li>{{ error }}</li>
                {% endfor %}
            </ul>
        {% endif %}
    </dd>
{% endmacro %}
        <form method="POST" action="{{ url_for('auth.login') }}">
            {{ render_field(form.email) }}
            {{ render_field(form.password) }}
            {{ render_field(form.remember_me) }}
            <input type="submit" value="login">
        </form>

 if form.validate_on_submit():

 #
if form.validate_on_submit():
    pass
else:
    print(form.errors)

 @auth.route('/login', methods=['GET', 'POST'])
def login():
    form = LoginForm()
    if form.validate_on_submit():
        pass
    else:
        print(form.errors)
        user = User.query.filter_by(email=form.email.data).first()
        if user is not None and user.verify_password(form.password.data):
            login_user(user, form.remember_me.data)
            return redirect(request.args.get('next') or url_for('main.index'))
        flash('Invalid user name or password!!')
    return render_template('auth/login.html', form=form)

 print(from.errors)

 HTTP/1.1” 302

 return redirect("http://google.com")

  <div class="page-header">
        <h1>Login</h1>
    </div>
    <div class="col-md-4">
        <form method="POST" class="form">
            {{ form.hidden_tag() }}
            {{ render_field(form.email) }}
            {{ render_field(form.password) }}
            {{ render_field(form.remember_me) }}
            {{ render_field(form.submit) }}
        </form>
    </div>
    <p>
        New user?
        <a href="{{ url_for('auth.register') }}">
            Click here to register
        </a>
    </p>