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How to debug uncalled __del__()

I use __del__() to write a warning log in case the object gets deleted while in a wrong internal state (please no wrath about it).

I tried to test it but although I use del my_object in the test, the __del__() doesn't seem to be called.

__del__()'s reference warns of 3 situations where this might happen, but doesn't give a clue on how to debug them.

So... How do I go about debugging it?

Solution

  • If __del__ is not being called when you invoke del myObject directly, then there is at least one other outstanding reference to myObject. I'm guessing you have stuffed it into a list or dict or set (or perhaps a memoizing cache), which does not copy the object, just saves a second reference to the original. Even doing:

    myObject = MyObjectClassWith__del__()
del myObject

    might not necessarily call __del__, if the class's __init__ method or __new__ method saves the new instance into some class-level cache or structure.

    Bottom line: check for other references, either by inspecting your code, or by using the weakref or gc methods posted in other answers.