Function for Python Django to update request.GET parameters, retaining all existing parameters, with a given parameter added or updated.

django_url_param_updater.py

def update_url_param(request, param_name):
    # function to update request.GET params, retaining all existing params, with param_name added or updated.
    existing_params = dict(request.GET)  # convert immutable querydict to mutable dict
    if not existing_params:
        return '?{}='.format(param_name)
    else:  # if existing params
        existing_str = ''
        existing_params.pop(param_name, None)  # pop off existing param_name if exists
        for p, v in existing_params.items():
            existing_str += '{}{}&'.format(p, '={}'.format(v[0]) if v[0] else '')
        return '?{}{}='.format(existing_str, param_name)

Use at your own risk. Works for my current needs, but not extensively tested.