I ran into some code recently where this pattern caused me so much headache - class A has an attribute which is an instance of class B, and class B has a "parent" attribute (which points to the instance of class A that class B is an attribute of):

  class Foo:
      def __init__(self, bar):
          self.bar = bar
  
  class Bar:
      def __init__(self, foo):
          self.foo = foo

Obviously both called into each other to do $THINGS... Pure madness.

So my suggestion: Try not to have interdependent classes :D

Well, at times having a parent pointer is rather useful! E.g. a callback registration will be able to unregister itself from everywhere where it has been registered to, upon request. (One would want to use weak references in this case.)

Fair point!

Maybe I am just a bit burned by this particular example I ran into (where this pattern should IMO not have been used).