docs: def get_model_by_name(model_name):
      """ Get model by its name.
  
      :param str model_name: name of model.
      :return django.db.models.Model:
  
      Example:
          get_concrete_model_by_name('auth.User')
          django.contrib.auth.models.User
  
      """
      if isinstance(model_name, six.string_types) and \
              len(model_name.split('.')) == 2:
          app_name, model_name = model_name.split('.')
  
          if django.VERSION[:2] < (1, 8):
              model = models.get_model(app_name, model_name)
          else:
              from django.apps import apps
              model = apps.get_model(app_name, model_name)
      else:
          raise ValueError("{0} is not a Django model".format(model_name))
  
      return model