Django filter to keep only wanted HTML tags

app_filters.py

from django import template
from django.utils.html import format_html
from django.template.defaultfilters import stringfilter

register = template.Library()

@register.filter(name='keeptags')
@stringfilter
def keeptags(value, tags):
    """
    Strips all [X]HTML tags except the space seperated list of tags
    from the output.

    Usage: keeptags:"strong em ul li"
    """
    import re
    from django.utils.html import strip_tags, escape
    tags = [re.escape(tag) for tag in tags.split()]
    tags_re = '(%s)' % '|'.join(tags)
    singletag_re = re.compile(r'<(%s\s*/?)>' % tags_re)
    starttag_re = re.compile(r'<(%s)(\s+[^>]+)>' % tags_re)
    endtag_re = re.compile(r'<(/%s)>' % tags_re)
    value = singletag_re.sub('##~~~\g<1>~~~##', value)
    value = starttag_re.sub('##~~~\g<1>\g<3>~~~##', value)
    value = endtag_re.sub('##~~~\g<1>~~~##', value)
    value = strip_tags(value)
    value = escape(value)
    recreate_re = re.compile('##~~~([^~]+)~~~##')
    value = recreate_re.sub('<\g<1>>', value)
    return format_html(value)