Private Class Variables in Python?

Question

I'd like to be able to extend a class without inheriting one of the class variables.

Given this scenario:

class A:
    aliases=['a','ay']

class B(A):
    pass

print(B.aliases)

I would rather get an error that B has not defined the aliases variable rather than have B accidentally called ay.

One could imagine a solution where aliases becomes a member of the instantiated object (self.aliases) and is set in __init__ but I really want to be able to access the aliases using the cls object rather than an instance of the class.

Any suggestions?

Answer 1

Python does not have REALY private attributes. But you can define it with a double underscore (__):

class A:
    __aliases=['a','ay']

class B(A):
    pass

print(B.__aliases) # yields AttributeError

But you still will be able to access it with:

print(B._A__aliases)