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python - Django + Python：会自动检测类型吗？

问题描述

我想知道我是否必须转换discount_value成小数（以确保）。似乎当我使用printdiscount_value 对其进行测试时，它的类型会自动检测为小数。但是，我之前遇到过一些情况，它被检测为浮点数并且不再起作用。

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

标签： python

解决方案

在将它传递给之前似乎没有必要做discount_valuea因为转换为. 出于同样的原因，注释行似乎是不必要的，但您的整个函数也是如此。为什么不这样做呢？Decimal()quantize()quantizeDecimal()quantize()

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")

另请注意：quantize()

与其他操作不同，如果量化操作后的系数长度大于精度，则会发出 InvalidOperation 信号。这保证了，除非存在错误条件，否则量化的指数总是等于右手操作数的指数。

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