Question

How or can I do the following? Please note that while I declare b_class, I don’t always directly instantiate b_class but is instantiated by a library.

class a_class:
  def some_method(self):
    """
    get the class instance of b_class in which a_class is instantiated
    using that instance, get var1
    perform some action based on var1
    """

class b_class:
  var1 = "init by the constructor or a method"
  a_inst = a_class()
  """
  other attributes
  """

Answer 1

You can’t, not without passing a reference to the instance of b_class when you call some_method or when you create your a_class instance.

You could store references to that a_class instance anywhere, and because of that, you cannot, in Python, know from within the instance method where it has been assigned.

So, do this:

class a_class:
  def __init__(self, parent):
    self.parent = parent

  def some_method(self):
    self.parent.var1

class b_class:
  def __init__(self):
      self.var1 = "init by the constructor or a method"
      self.a_inst = a_class(self)

Now instances of a_class ‘know’ about their parent, and can reference them via the self.parent instance variable.