Python 为什么克隆FloatField的这个子类（添加了验证程序）会引发异常？

我不熟悉Python和Django

我希望我的模型具有经过范围验证的浮动。根据我写的：

class FloatRangeField (FloatField):
    """A FloatField constrained to a given range."""

    def __init__ (self, minimum, maximum, **kwargs):

        minmax = [MinValueValidator (minimum), MaxValueValidator (maximum)]

        print ("\n\t\tFloatRangeField({},{})".format(minimum,maximum)) # (A)
        FloatField.__init__ (self, validators = minmax, **kwargs)
        print ("\t\tFINISHED\n")

这在

python3 manage.py migrate

中导致了错误，我将其缩小为

clone（）

调用。演示：

print ("HERE 1")
tmp1 = FloatRangeField (10, 20)
print ("HERE 2")
tmp2 = FloatRangeField (10, 20)
print ("HERE 3")
tmp3 = tmp1.clone ()      # (B)
print ("HERE 4")

它从第

#（B）

行抛出异常。奇怪的是，当这种情况发生时，第

#（A）

行的跟踪没有打印出来。以下是输出：

HERE 1

                FloatRangeField(10,20)
                FINISHED

HERE 2

                FloatRangeField(10,20)
                FINISHED

HERE 3
Traceback (most recent call last):
  File "manage.py", line 15, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.5/dist-packages/django/core/management/__init__.py", line 371, in execute_from_command_line
    utility.execute()

[...snip...]

    tmp3 = tmp1.clone ()
  File "/usr/local/lib/python3.5/dist-packages/django/db/models/fields/__init__.py", line 470, in clone
    return self.__class__(*args, **kwargs)
TypeError: __init__() missing 2 required positional arguments: 'minimum' and 'maximum'

为什么会出现这种情况？我应该如何实现

FloatRangeField

，以封装最小/最大验证器的功能？

类似的内容写在：

如果您添加一个新的关键字参数，您需要编写代码将其值放入

kwargs

您自己（…）

所以你也应该添加解构器。这是必需的，例如，要在迁移文件中表示此字段：

class FloatRangeField (FloatField):
    """A FloatField constrained to a given range."""

    def __init__ (self, minimum, maximum, **kwargs):
        self.minimum = minimum
        self.maximum = maximum
        minmax = [MinValueValidator (minimum), MaxValueValidator (maximum)]
        FloatField.__init__ (self, validators = minmax, **kwargs)

    def deconstruct(self):
        result = __, __, __, kwargs = super(FloatRangeField, self).deconstruct()
        kwargs['minimum'] = self.minimum
        kwargs['minimum'] = self.maximum
        del kwargs['validators']
        return result

---

因此，在这里我们在

解构（…）

函数中，我们删除了前两个验证器（我们在

\uuuu init\uuuu（…）

函数中添加的验证器）。

错误很明显：它无法克隆字段，因为缺少两个参数。

class FloatRangeField (FloatField):
    """A FloatField constrained to a given range."""

    def __init__ (self, minimum, maximum, **kwargs):
        self.minimum = minimum
        self.maximum = maximum
        minmax = [MinValueValidator (minimum), MaxValueValidator (maximum)]
        FloatField.__init__ (self, validators = minmax, **kwargs)

    def deconstruct(self):
        result = __, __, __, kwargs = super(FloatRangeField, self).deconstruct()
        kwargs['minimum'] = self.minimum
        kwargs['minimum'] = self.maximum
        del kwargs['validators']
        return result

class FloatRangeField (FloatField):
    """A FloatField constrained to a given range."""

    def __init__ (self, minimum, maximum, **kwargs):
        self.minimum = minimum
        self.maximum = maximum
        old_validators = kwargs.get('validators', [])
        minmax = [MinValueValidator (minimum), MaxValueValidator (maximum)]
        kwargs['validators'] = minmax + old_validators
        FloatField.__init__ (self, **kwargs)


    def deconstruct(self):
        result = __, __, __, kwargs = super(FloatRangeField, self).deconstruct()
        kwargs['minimum'] = self.minimum
        kwargs['minimum'] = self.maximum
        kwargs['validators'] = kwargs['validators'][2:]
        return result