I am working on optimization problems. As you know, optimization is an iterative process. Some sections are selected, and the weight of all sections is calculated.
I have code like this:
class Test:
W = 0
def __init__(self, l, A):
self.l = l
self.A = A
Test.W += self.A * self.l
instance1 = Test(5, 10)
instance2 = Test(3, 7)
instance3 = Test(6, 13)
print(Test.W)
instance1.A = 20
instance2.A = 30
instance3.A = 40
print(Test.W)
At creation of instances 1-3, the program calculated 149 for W. It is correct.
But if I change A values, the result is 149 again and again.
How can I update the class attribute W when I change A or l?
If you want modifications made to an instance attribute to effect the value of a class attribute, you can make the instance attribute a property and place the additional logics in its setter method instead:
class Test:
W = 0
def __init__(self, l, A):
self.l = l
self.A = A
@property
def A(self):
try:
return self._A
except AttributeError:
return 0
@A.setter
def A(self, value):
Test.W += (value - self.A) * self.l
self._A = value
so that:
instance1 = Test(5, 10)
instance2 = Test(3, 7)
instance3 = Test(6, 13)
print(Test.W)
instance1.A = 20
instance2.A = 30
instance3.A = 40
print(Test.W)
outputs:
149
430