这是一个令人不安的问题.对于功能：

def influencePositive(q1,q2):
    if(q1.magnitude.greaterZero()):
        q2.derivative.value = DValue.add(q2.derivative.value,1)

以下单元测试运行没有问题：

def test_i_plus_active(self):
        q1 = Quantity(Magnitude(MValue.PLUS),None)
        q2 = Quantity(None,Derivative(DValue.ZERO))

        r.influencePositive(q1,q2)
        self.assertEqual(q2.derivative.value,DValue.PLUS)

但是对于其他功能：

def exogenous(q1,q2,value):
    if type(value) == int:
        q2.derivative.value = DValue.add(q1.derivative.value,value)

以下单元测试中断：

def test_ex_increase_minus(self):
        q1 = Quantity(None,DValue.MINUS)
        q2 = Quantity(None,DValue.MINUS)

        r.exogenous(q1,1)
        self.assertEqual(q2.derivative.value,DValue.ZERO)

它将引发Atribute错误：AttributeError：无法设置属性.那就是整个回溯：

Traceback (most recent call last):
  File "C:/Users/Victor Zuanazzi/Documents/Artificial Intelligence/Knowledge Representation/Practicals/Qualitative_Reaoning/relationFunction_test.py",line 121,in test_ex_increase_minus
    r.exogenous(q1,1)
  File "C:\Users\Victor Zuanazzi\Documents\Artificial Intelligence\Knowledge Representation\Practicals\Qualitative_Reaoning\relationFunctions.py",line 31,in exogenous
    q2.derivative.value = DValue.add(q1.derivative.value,value)
  File "C:\ProgramData\Anaconda3\lib\types.py",line 146,in __set__
    raise AttributeError("can't set attribute")
AttributeError: can't set attribute

这里是一些了解上面代码的背景知识.

DValue是一个IntEnum：

from enum import IntEnum

class DValue(IntEnum):
    MINUS = -1
    ZERO = 0
    PLUS = 1

    @staticmethod
    def add(dvalue,delta):
        return max(min(dvalue + delta,DValue.PLUS),DValue.MINUS)

我们使用它来设置派生类：

class Derivative:
    def __init__(self,value):

        #if value is type int,it is converted to Enum.
        if value is int:
            value = DValue(value)

        self.value = value

数量是一类,具有为其实例设置的大小和派生值：

from magnitude import Magnitude,MValue
from derivative import Derivative,DValue

class Quantity:
    def __init__(self,magnitude,derivative):
        self.magnitude = magnitude
        self.derivative = derivative

我不明白为什么ImpactPositive()可以正常工作,而exogenous()可以中断.它们都以相同的方式调用DValue.add().