Ports Django 5.1's `{% querystring %}` template tag functionality to Jinja2.

jinja2.py

# config/jinja2.py

"""
Ports Django 5.1's `{% querystring %}` template tag (https://docs.djangoproject.com/en/5.1/releases/5.1/#querystring-template-tag)
to a Jinja2 global function for `django-jinja`.

Add this to `config/jinja2.py`, then in your settings file:
TEMPLATES = [
    {
        'BACKEND': 'django_jinja.jinja2.Jinja2',
        'OPTIONS': {
            'globals': {
                'querystring': 'config.jinja2.querystring',
            },
        },
    },
]
"""

from collections.abc import Iterable

from jinja2 import pass_context


@pass_context
def querystring(context, query_dict=None, **kwargs):
    """
    Add, remove, and change parameters of a ``QueryDict`` and return the result
    as a query string. If the ``query_dict`` argument is not provided, default
    to ``request.GET``.

    For example::

        {{ querystring(foo=3) }}

    To remove a key::

        {{ querystring(foo=None) }}

    To use with pagination::

        {{ querystring(page=page_obj.next_page_number) }}

    A custom ``QueryDict`` can also be used::

        {{ querystring(my_query_dict, foo=3) }}
    """
    if query_dict is None:
        try:
            query_dict = context['request'].GET
        except KeyError as e:
            msg = 'The `querystring` function requires `request` object in the context.'
            raise KeyError(msg) from e
    query_dict = query_dict.copy()
    for key, value in kwargs.items():
        if value is None:
            if key in query_dict:
                del query_dict[key]
        elif isinstance(value, Iterable) and not isinstance(value, str):
            query_dict.setlist(key, value)
        else:
            query_dict[key] = value
    if not query_dict:
        return ''
    query_string = query_dict.urlencode()
    return f'?{query_string}'