{{ form.flag.label }}
{% if form.flag.errors %} {{ form.flag(class_="form-control has-validation is-invalid", size=50) }}
{% else %} {{ form.flag(class_="form-control has-validation ", size=50) }}
{% endif %} {% for error in form.flag.errors %} [{{ error }}] {% endfor %}

{{ form.submit(class_="form-control") }}