title: Django templates: how to concatenate a named URL and a string?
body: <p>I have the following settings:</p>
  
  <p>The <code>urls.py</code> of the project's app:</p>
  
  <pre><code>urlpatterns = [
      url(r'^main/', include('main.urls', namespace='main')),
  ]
  </code></pre>
  
  <p>The <code>main</code> app's <code>urls.py</code>:</p>
  
  <pre><code>urlpatterns = [
      url(r'^add/$', views.add, name='add'),
  ]
  </code></pre>
  
  <p>I am trying to create an URL as <code>/main/add/whatever/</code> in a template, hypothetically as follows:</p>
  
  <pre><code>&lt;form method="POST" action="{% url 'main:add' %}" + "whatever/"&gt;
  </code></pre>
  
  <p>How do I do that?</p>