更改某些变量的值后更改条件

Question

i have this situation: a list of variables initially set to none A = [none, none, none, none] and a very simple function that controls if 2 values (different to none) are different:

def notEqual(a, b):
   if a is None and b is None:
       return True
   if a != b:
       return True
   return False

I want create a list named bigList that shows for each couple of element of A if they are equal or not. So i thought to do this:

for i in range(4):
   for j in range(4):
      if i != j:
         c = ((i, j), (notEqual(A[i], A[j])))
         bigList.append((c))

So at the beginning all the element of bigList are ((i,j), (True)) In a second moment i have this situation:

A[0]=10 A[1]=10

So the condition associated to (0,1) and (1,0) have to change to False. Is there an easy way to do something like this? (Change some conditions when some variables change their values)

Answer 1

No, there is no way. In most languages, expression are evaluated with current values of the variables. You can't make an expression that works like not_equal(current_value_of_A, current_value_of_B) that will automatically change when values of A and/or B change. So, in one way or another, you have to re-run your code.

A common way of doing something similar is the observer pattern . That is, wrap your expression in a class and notify the class when the value of something changes.

Along with that, use a dict instead of a list, which has the form {(i,j): notEqual(A[i], A[j]) , so you can update only the individual (i, j) pair without re-running your whole code

Answer 2

You, can use @propery of python. It works like getter similar to other languages like C# and JAVA.

In your case you can make a object similar to that of ((i, j), (notEqual(A[i], A[j]))) with a getter.

See sample implementation below

class bigListElement(object):
    A = [] # this is static
    def __init__(self, index_tuple, areEqual):
        self.index_tuple = index_tuple
        self._areEqual = areEqual

    @staticmethod
    def notEqual(a, b):
        if a is None and b is None:
            return True
        if a != b:
            return True
        return False

    @property
    def areEqual(self):
        return bigListElement.notEqual(bigListElement.A[self.index_tuple[0]], bigListElement.A[self.index_tuple[1]])


print("Hello World")

bigListElement.A = [10, 2, 10, 3, 4]
a = bigListElement((0, 1), False)

print(a.areEqual) # True

bigListElement.A[1] = 10

print(a.areEqual) # False