<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add_quantity(self, quantities, value, source, check_for_dupes=True, compare_to_existing=True, **kwargs):
 """Add an `Quantity` instance to this entry."""

        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