can someone explain this __del__ behaviour?

[rjdegraff42]

I came across something interesting that I can't explain. Perhaps someone here can. When the following code is run with the lambda commented out it produces the output I expect to see.

    class Exp:
        def __init__(self):
            print('__init__')
            self.b = 1
            #self.a = lambda: self.b

        def __del__(self):
            print('__del__')

    obj = Exp()
    obj = None

Output

    __init__
    __del__

But with the lambda uncommented

    class Exp:
        def __init__(self):
            print('__init__')
            self.b = 1
            self.a = lambda: self.b

        def __del__(self):
            print('__del__')

    obj = Exp()
    obj = None

I do not see that __del__ is executed.

    __init__

As I understand it, __del__ executes when the reference count for an object reaches zero so I can only assume that somehow the lambda line is doing something odd. But if I modify the lambda to

    class Exp:
        def __init__(self):
            print('__init__')
            self.b = 1
            self.a = lambda: 10

        def __del__(self):
            print('__del__')

    obj = Exp()
    obj = None

I get

    __init__
    __del__

I'm not a fan of lambdas, but typically a lambda specifies a parameter and something that operates on that parameter like

    self.a = lambda x: x**2

so perhaps specifying self.b in the lambda expression is causing a problem with the reference counter.