Chapter 18: Building Forms and Reusable UI Helpers

ASP.NET Core Tag Helpers reduce repetitive form markup. In Python/Jinja2, use macros, partial templates, or a form library.

Jinja2 macro:

{% macro field(name, label, value="", errors=[]) %}
  <label for="{{ name }}">{{ label }}</label>
  <input id="{{ name }}" name="{{ name }}" value="{{ value|e }}">
  {% if errors %}
    <p class="error">{{ errors[0] }}</p>
  {% endif %}
{% endmacro %}

Use it:

{% from "forms.html" import field %}

{{ field("title", "Title", form.title, errors.title) }}

Good helper design:

• Keep helpers visual, not business-aware.
• Let handlers decide data and validation.
• Prefer a small set of project macros over a large custom template framework.
• For complex form-heavy apps, evaluate Django forms before building your own mini-framework.