[django, jinja2, coffin] Add query string parameters to current URL

url_add_query.py

from jinja2 import nodes
from jinja2.ext import Extension


class UrlAddQueryExtension(Extension):
    """Add query string parameters to the current URL

    This is a Jinja2 version of http://djangosnippets.org/snippets/2882/
    targeted to work for django+coffin.
    The django request object must be included in the context.

    usage:
        {% url_add_query page=pager.next_page_number() %}
    """
    tags = set(['url_add_query'])

    def parse(self, parser):
        stream = parser.stream
        tag = stream.next()

        kwargs = []
        while not stream.current.test_any('block_end', 'name:as'):
            if stream.current.test('name') and stream.look().test('assign'):
                key = nodes.Const(stream.next().value)
                stream.skip()
                value = parser.parse_expression()
                kwargs.append(nodes.Pair(key, value, lineno=key.lineno))

        return nodes.Output([
            self.call_method('_render', args=[nodes.Name('request', 'load'), nodes.Dict(kwargs)]),
        ]).set_lineno(tag.lineno)

    def _render(self, request, kwargs):
        get = request.GET.copy()
        get.update(kwargs)

        path = '%s?' % request.path
        for query, val in get.items():
            path += '%s=%s&' % (query, val)

        return path[:-1]