将数字除以 Python 中我的 class 的实例

Question

我有一个名为 Time 的 class，我需要实现一个 Frequency class。如何实现将 ints 或 floats 除以 Time 的实例以获得 Frequency 的实例？

我已经知道 __div__、__truediv__、__floordiv__ 和其他 Python 特殊方法，并且我已经在我的代码中使用它们来划分 classes 按数字或其他 classes 的实例，但我找不到将数字除以我的 class.

实例的方法

是否可以实现将数字除以 Python 中的 class 的实例？

Answer 1

您需要实施 __rtruediv__ 和 __rfloordiv__。

来自 the documentation

object.__radd__(self, other)
object.__rsub__(self, other)
object.__rmul__(self, other)
object.__rmatmul__(self, other)
object.__rtruediv__(self, other)
object.__rfloordiv__(self, other)
object.__rmod__(self, other)
object.__rdivmod__(self, other)
object.__rpow__(self, other)
object.__rlshift__(self, other)
object.__rrshift__(self, other)
object.__rand__(self, other)
object.__rxor__(self, other)
object.__ror__(self, other)

These methods are called to implement the binary arithmetic operations (+, -, *, @, /, //, %, divmod(), pow(), **, <<, >>, &, ^, |) with reflected (swapped) operands. These functions are only called if the left operand does not support the corresponding operation [3] and the operands are of different types. [4] For instance, to evaluate the expression x - y, where y is an instance of a class that has an __rsub__() method, y.__rsub__(x) is called if x.__sub__(y) returns NotImplemented.

Answer 2

__rtruediv__ 方法正是您要找的。 x / y执行时，如果type(x)没有实现__div__(self, other)方法，其中other可以是classtype(y)，那么type(y).__rtruediv__(y, x)被执行，返回结果。

用法：

class Foo:
    def __init__(self, x):
        self.x = x

    def __truediv__(self, other):
        return self.x / other

    def __rtruediv__(self, other):
        return other / self.x

>>> f = Foo(10)    
>>> f / 10
1.0
>>> 10 / f
1.0

Answer 3

是的。您只需要确保 Time.__rtruediv__() return 在收到浮点数或整数时是一个 Frequency 实例。

用法：

>>> 100 / Time(2)
Frequency(50.0)
>>> 2.5 / Time(5)
Frequency(0.5)

实施：

class Time:
  def __init__(self, value):
    self.value = value

  def __rtruediv__(self, other):
    if not isinstance(other, (int, float)):
      return NotImplemented
    return Frequency(other / self.value)

class Frequency:
  def __init__(self, value):
    self.value = value

  def __repr__(self):
    return '{}({})'.format(self.__class__.__name__, self.value)

python 文档包含有关 implementing the arithmetic operations 的完整示例，供您自定义类。

处理不兼容类型的正确方法是 return 特殊值 NotImplemented。

NotImplemented

Special value which should be returned by the binary special methods (e.g. __eq__(), __lt__(), __add__(), __rsub__(), etc.) to indicate that the operation is not implemented with respect to the other type

假设您尝试使用不受支持的复数，returning NotImplemented 最终会导致 TypeError 并显示正确的错误消息。（至少在 python 3）

>>> 100j / Time(2)

Traceback (most recent call last):
  File "python", line 1, in <module>
TypeError: unsupported operand type(s) for /: 'complex' and 'Time'

将数字除以 Python 中我的 class 的实例

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