def clean_quantity(self, quantity):
return _clean_quantity(quantity, self.max_quantity)<EOL>
Check and normalize the quantity.

        The following checks are performed:

            * the quantity can be converted to an integer
            * it's positive
            * it's doesn't exceed the value of :attr:`max_quantity`

        Parameters
        ----------
        quantity : int-convertible

        Returns
        -------
        int
            The normalized quanity.

        Raises
        ------
        NegativeItemQuantity
        NonConvertibleItemQuantity
        TooLargeItemQuantity
        ZeroItemQuantity