Question

我想知道是否必须将discount_value转换为小数（以确保）。看来，当我使用print discount_value对其进行测试时，它的类型会自动检测为十进制。但是，我以前有过一些案例，在该案例中，它被检测为浮动对象，并且不再起作用。

def calculate_discounted_value(self, ticket_price_gross):
        [...]

        elif self.percentage:
            discount_value = Decimal(ticket_price_gross * self.percentage)
            discount_value = quantize(discount_value, '1')
            print(ticket_price_gross - discount_value, "PERCENTAGE")

def quantize(amount, decimals):
    """
    Decimal numbers can be represented exactly. In contrast, numbers like 1.1 and
    2.2 do not have exact representations in binary floating point. End users
    typically would not expect 1.1 + 2.2 to display as 3.3000000000000003 as it
    does with binary floating point. With this function we get better control about
    rounding.

    Therefore: amount should be come in as decimal.
    """
    #amount_as_decimal = Decimal(amount)
    amount_as_decimal = amount
    quantized_amount = amount_as_decimal.quantize(
        Decimal(decimals),
        rounding=ROUND_HALF_UP
    )
    return quantized_amount

Answer 1

由于discount_value转换为Decimal()，因此在将quantize()转换为quantize之前似乎没有必要将Decimal()设为quantize()。出于同样的原因，注释行似乎不必要，但是整个def calculate_discounted_value(self, ticket_price_gross): [...] elif self.percentage: discount_value = Decimal(ticket_price_gross * self.percentage).quantize(Decimal(1), rounding='ROUND_HALF_UP') print(ticket_price_gross - discount_value, "PERCENTAGE")函数也是如此。为什么不这样做呢？

quantize()

还要注意&的{{3}}：

与其他运算不同，如果后的系数长度量化操作将大于精度，然后发出InvalidOperation信号。这样可以保证，除非存在错误条件下，量化指数始终等于右手操作数。

Django + Python：会自动检测类型吗？

1 个答案: