from django import template
from django.utils.safestring import mark_safe
import markdown
register = template.Library()
@register.filter
def currency(value):
"""Format number as currency."""
try:
return f'${float(value):,.2f}'
except (ValueError, TypeError):
return value
@register.filter
def percentage(value, decimals=1):
"""Format number as percentage."""
try:
return f'{float(value):.{decimals}f}%'
except (ValueError, TypeError):
return value
@register.filter(is_safe=True)
def markdown_to_html(text):
"""Convert markdown to HTML."""
if not text:
return ''
return mark_safe(markdown.markdown(text))
@register.filter
def truncate_chars(value, length=100):
"""Truncate string to length with ellipsis."""
if len(value) <= length:
return value
return value[:length].rsplit(' ', 1)[0] + '...'
{% load custom_filters %}
<p>Price: {{ product.price|currency }}</p>
<p>Discount: {{ discount|percentage:2 }}</p>
<div class="content">
{{ post.content|markdown_to_html }}
</div>
<p>{{ long_text|truncate_chars:150 }}</p>
Custom template filters transform variables in templates. I decorate functions with @register.filter and optionally set is_safe=True for HTML output. Filters take one or two arguments. For formatting dates, numbers, or text, filters keep logic out of views. I use stringfilter decorator for string-only filters. Built-in filters cover most cases, but custom ones handle domain-specific formatting. This keeps templates clean and promotes reusability across templates.
