Login page not working - 'form' referenced before assignment

@app.route('/login', methods=('GET', 'POST'))
def login():
    form = form.LoginForm()
    if form.validate_on_submit():
        try:
            user = models.User.get(models.User.email == form.email.data)
        except models.DoesNotExist:
            flash("Your email or password doesn't match!", "error")
        else:
            if check_password_hash(user.password, form.password.data):
                login_user(user)
                flash("You've been logged in!", "success")
                return redirect(url_for('index'))
            else:
                flash("Your email or password doesn't match!", "error")
    return render_template('login.html', form=form)

class LoginForm(Form):
    email = StringField('Email', validators=[DataRequired(), Email()])
    password = PasswordField('Password', validators=[DataRequired()])

{% from 'macros.html' import render_field %}
<form method="POST" action="" class="form">
    {{ form.hidden_tag() }}
    {% for field in form %}
        {{ render_field(field) }}
    {% endfor %}
    <button type="submit" id="submit">Login!</button>
</form>