I have the following code in Python 3:
class x():
var = 0
x1 = x()
x2 = x()
print(x.var) #0
print(x1.var) #0
print(x2.var) #0
But if I change the attribute var for one instance, it change only for this instance:
x1.var = 1
print(x.var) #0
print(x1.var) #1
print(x2.var) #0
I would like the result to be:
x1.var = 1
print(x.var) #1
print(x1.var) #1
print(x2.var) #1
An instance attribute can shadow a class attribute of the same name. If you want to change a class attribute via an instance, you have to do so explicitly, by getting a reference to the class. Otherwise, you are just creating a new instance attribute, rather than updating the class attribute.
class X:
var = 0
x1 = X()
x2 = X()
type(x1).var = 1
Building on the comment of @khelwood, you can change the class attribute by referencing instance.__class__:
class x():
var = 0
x1 = x()
x2 = x()
print(x.var) #0
print(x1.var) #0
print(x2.var) #0
x1.__class__.var = 1
print(x.var) #1
print(x1.var) #1
print(x2.var) #1
x.var, usex.var = 1.x1.var = ...to change a class attribute, you'll need to define a setter that explicitly sets the class attribute.