Question

Is there a way, in Python, to do something like this?

class A():
    var = "1, 2, 3"

class B():
    var = ... ", 4"


instance = B()
instance.var # = 1, 2, 3, 4

Answer 1

The example given in the question uses neither a superclass nor an instance variable. From the title of the question, presumably you wanted to use both. Here’s an example of how it would work:

class A(object):
  def __init__(self):
    self.var = "1,2,3"

class B(A):
  def __init__(self):
    super(B,self).__init__()
    self.var += ",4,5"

print A().var
print B().var

Note that your example simply assigns attributes to unrelated classes, using the classes sort-of like namespaces. Which is perfectly reasonable, but not quite what you asked:

class A:
  var = "1,2,3"

class B:
  var = A.var + ",4,5"

print A.var
print B.var