code: def primary_avatar(user, size=AVATAR_DEFAULT_SIZE):
      
      alt = unicode(user)
      url = reverse('avatar_render_primary', kwargs={'user' : user, 'size' : size})
      return """<img src="%s" alt="%s" />""" % (url, alt,
          )
docs: This tag tries to get the default avatar for a user without doing any db
      requests. It achieve this by linking to a special view that will do all the 
      work for us. If that special view is then cached by a CDN for instance,
      we will avoid many db calls.