code: def user_stats(request):
      
      user = get_user_id(request)
      language = get_language(request)
  
      concepts = None    # meaning all concept
      if "concepts" in request.GET:
          concepts = Concept.objects.filter(lang=language, active=True,
                                            identifier__in=load_query_json(request.GET, "concepts"))
      data = UserStat.objects.get_user_stats(user, language, concepts)
      return render_json(request, data, template='concepts_json.html', help_text=user_stats.__doc__)
docs: JSON of user stats of the user
  
      GET parameters:
        html (bool):
          turn on the HTML version of the API, defaults to false
        user (int):
          identifier of the user, defaults to logged user
        concepts (list):
          list of identifiers of concepts, defaults to all concepts
        lang (str):
          language of requested concepts, defaults to language from django