How to subtract one decimal from another.

Using Django
1

I have a model with the following:

regular_price = models.DecimalField(

        verbose_name=("Regular price"),

        help_text=("Price you which to sell the product"),

        error_messages={

            "name": {

                "max_length": ("The price you want to sell the product"),

            },

        },

        max_digits=10,

        decimal_places=2, default=0

    )

    discount_price = models.DecimalField(

        verbose_name=("Discount price"),

        help_text=(

            "The amount you want to remove from the actual price, leave to reduce nothing"),

        error_messages={

            "name": {

                "max_length": ("you can leave or put the price you want to reduce."),

            },

        },

        max_digits=10,

        decimal_places=2, blank=True, null=True

Now I have a function that calculates the actual price:

    def actual_price(self):
        price = (self.regular_price)-(self.discount_price)
        return price

when I call the function (actual_price) from the front end, I keep receiving the following error message:

unsupported operand type(s) for -: ‘decimal.Decimal’ and ‘NoneType’

My question is that what is the proper way to perform subtraction of decimals in django?

2

I have gotten the reason for the error, I simply need to give a default value of 0 to the discount_price, this will make it possible for any mathematical calculation to occur.