code: def add_quantity(self,
                       quantities,
                       value,
                       source,
                       check_for_dupes=True,
                       compare_to_existing=True,
                       **kwargs):
          
          success = True
          for quantity in listify(quantities):
              kwargs.update({QUANTITY.VALUE: value, QUANTITY.SOURCE: source})
              cat_dict = self._add_cat_dict(
                  Quantity,
                  quantity,
                  compare_to_existing=compare_to_existing,
                  check_for_dupes=check_for_dupes,
                  **kwargs)
              if isinstance(cat_dict, CatDict):
                  self._append_additional_tags(quantity, source, cat_dict)
                  success = False
  
          return success
docs: Add an `Quantity` instance to this entry.