Django URLS, using a ? in the URL

You don't match these against the regex. The elements after the ? are not part of the URL, they are query parameters which can be accessed from your view via request.GET.

? won't match an "?" inside the url , instead it has its own meaning which you can look it up here :
Python Regular Expressions If you want to match the exact character of "?" inside your url , you have to somehow escape it ( cause it has a meaning in RegExs ) so you might wanna escape it by a "\" (a backslash ) so you would write \?sort ....

EDIT :
Okay so with what you've said in comments , seems here's your problem , main?sort=popular occurs on your url pattern when you are rendering the template for /main/ with the GET method dictionary argument of sort=popular, just write a function that distinguishes between GET and POST , in the GET part , have sth like sort_by = request.GET.get('sort','') and then sort accordingly with the value of sort_by variable, would be sth like :

def main_handler(request):
     if request.method == "POST":
           whatever ... 
     if request.method == "GET" :
           sort_by = request.GET.get('sort','')
           if sort_by:
                 sort by what sort points to 
                 return "the sorted template"
     return render_to_response(the page and it's args)

and let go of that ? inside the url pattern , that's added when you request a page with a GET argument.