The selected answer is out of date and no others worked for me (Django 1.6 and [apparantly] no registered namespace.)
For Django 1.5 and later (from the docs)
Warning
Don’t forget to put quotes around the function path or pattern name!
With a named URL you could do:
(r'^login/', login_view, name="login"),
...
<a href="{% url 'login' %}">logout</a>
Just as easy if the view takes another parameter
def login(request, extra_param):
...
<a href="{% url 'login' 'some_string_containing_relevant_data' %}">login</a>