Django template tag to highlight the active navigation item

active_nav_tag.py

@register.simple_tag(takes_context=True)
def active_nav(context, pattern_or_urlname, is_sr_text=False):
    path = context['request'].path
    if ',' in pattern_or_urlname:
        patterns_to_try = pattern_or_urlname.split(',')
    else:
        patterns_to_try = [pattern_or_urlname]
    for pattern in patterns_to_try:
        try:
            p = '^' + reverse(pattern)
        except NoReverseMatch:
            p = pattern
        if re.search(p, path):
            if is_sr_text:
                return mark_safe(' <span class="sr-only">(current)</span>')
            else:
                return ' active'
    return ''

# Based on this Stack Overflow answer: https://stackoverflow.com/a/18772289
# Designed for use with Bootstrap, use this template tag in your primary navigation menu
# to indicate to the user which navigation item is currently selected. 
#
# Usage: Call this tag along with the name of the url pattern or the url or url fragment
# for the item path of the navigation item. To check multiple urls pass in a comma-separated
# list of patterns or urls.
# 
# Returns: By default, this will return ' active' if the requested url is in the requested url.
# Use this as a CSS class on your navigation item to visually highlight the navigation item. 
# Pass in `True` for is_sr_text to instead return ' <span class="sr-text">(current)</span>' to
# use in the text of the navigation item to alert screen readers that the navigation item is 
# selected.
#
# Examples:
# <ul class="navbar-nav mr-auto">
#     <li class="nav-item{% active_nav 'main:about' %}">
#         <a class="nav-link" href="{% url 'main:about' %}">About{% active_nav 'main:about' True %}</a>
#     </li>
#     <li class="nav-item{% active_nav 'main:contact' %}">
#         <a class="nav-link" href="{% url 'main:contact' %}">About{% active_nav 'main:contact' True %}</a>
#     </li>
#     <li class="nav-item dropdown{% active_nav 'users,organizations' %}">
#         <a class="nav-link dropdown-toggle" href="#" id="myProfileButton" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
#             Hi {{ user.get_short_name }}{% active_nav 'users,organizations' True %}
#         </a>
#         <div class="dropdown-menu" aria-labelledby="myProfileButton">
#             <!-- ... -->
#         </div>
#     </li>
# </ul>
#
# Limitations: Currently this does a search only to see if the request path contains the url
# pattern, instead of checking for an exact match, which may result in false positives.

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