Jinja2 macros to render simple WTForms form with Bulma

form.html

{% macro field_description(field) %}
{% if field.errors %}
{% for error in field.errors %}
<p class="help is-danger">{{ error }}</p>
{% endfor %}
{% else %}
{% if field.description %}
<p class="help is-italic">{{ field.description }}</p>
{% endif %}
{% endif %}
{% endmacro %}


{% macro render_field(field) %}
<div class="field is-horizontal">
  <div class="field-label">
    {% if field.widget.input_type not in ('checkbox', 'radio') %}
    <label class="label">{{ field.label.text|safe }}{% if field.flags.required %} <span class="has-text-danger has-text-weight-bold">*</span>{% endif %}</label>
    {% endif %}
  </div>
  <div class="field-body">
    {% if field.widget.input_type in ('checkbox', 'radio') or field.type == 'SelectField' %}
    <div class="field is-narrow">
      <div class="control">
        {% if field.type == 'SelectField' %}
        <div class="select is-fullwidth">
          {{ field(**kwargs) }}
        </div>
        {% else %}
        <label class="{{ field.widget.input_type }}">
          {{ field(**kwargs) }} {{ field.label.text|safe }}
        </label>
        {% endif %}
      </div>
      {{ field_description(field) }}
    </div>
    {% else %}
    <div class="field">
      <div class="control">
        {% if field.type == 'TextAreaField' %}
        {{ field(class_='textarea') }}
        {% else %}
        {{ field(class_='input', **kwargs) }}
        {% endif %}
      </div>
      {{ field_description(field) }}
    </div>
    {% endif %}
  </div>
</div>
{% endmacro %}

{% macro form_errors(form, hiddens=True) %}
{%- if form.errors %}
  {%- for fieldname, errors in form.errors.items() %}
    {%- if (is_hidden_field(form[fieldname]) and hiddens) or (not is_hidden_field(form[fieldname]) and hiddens != 'only') %}
      {%- for error in errors %}
        <div class="help is-danger">{{ error }}</div>
      {%- endfor %}
    {%- endif %}
  {%- endfor %}
{%- endif %}
{%- endmacro %}

{% macro render_form_fields(form) %}
{{ form.hidden_tag() }}
{{ form_errors(form, hiddens='only') }}
{%- for field in form %}
  {% if not is_hidden_field(field) -%}
    {{ render_field(field) }}
  {%- endif %}
{%- endfor %}
{%- endmacro %}

{% macro render_form_buttons(buttons) %}
<div class="field is-horizontal">
  <div class="field-label"></div>
  <div class="field-body">
    <div class="field">
      <div class="control">
        {%- for button in buttons %}
        {{ button.render() }}&nbsp;
        {%- endfor %}
      </div>
    </div>
  </div>
</div>
{%- endmacro %}

{% macro render_form(form, action, width=6, box=True) %}
<div class="container">
  <div class="columns is-centered">
    <div class="column is-{{ width }}">
      <form method="post" action="{{ action }}" role="form" novalidate{% if box %} class="box"{% endif %}>
        {{ render_form_fields(form) }}
        {{ render_form_buttons(form.buttons) }}
      </form>
    </div>
  </div>
</div>
{%- endmacro %}

How are the form.buttons created? Don't see this anywhere in the WTForms documentation.

This is generic object, like in this example -> https://github.com/zgoda/bip/blob/master/src/bip/utils/forms.py#L55