Question

I have someting like this

class A:
  __a = 0
  def __init__(self):
    A.__a = A.__a + 1
  def a(self):
    return A.__a

class B(A):
  def __init__(self):
    # how can I access / modify A.__a here?
    A.__a = A.__a + 1 # does not work
  def a(self):
    return A.__a

Can I access the __a class variable in B? It’s possible writing a instead of __a, is this the only way? (I guess the answer might be rather short: yes 🙂

Answer 1

So, __a isn’t a static variable, it’s a class variable. And because of the double leading underscore, it’s a name mangled variable. That is, to make it pseudo-private, it’s been automagically renamed to _<classname>__<variablename> instead of __<variablename>. It can still be accessed by instances of that class only as __<variablename>, subclasses don’t get this special treatment.

I would recommend that you not use the double leading underscore, just a single underscore to (a) mark that it is private, and (b) to avoid the name mangling.