Python object deleting itself

Question

Why won\'t this work? I\'m trying to make an instance of a class delete itself.

>>> class A():
    def kill(self):
        del self


>>>          


        

Answer 1

I think I've finally got it!
NOTE: You should not use this in normal code, but it is possible. This is only meant as a curiosity, see other answers for real-world solutions to this problem.

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Take a look at this code:

# NOTE: This is Python 3 code, it should work with python 2, but I haven't tested it.
import weakref

class InsaneClass(object):
    _alive = []
    def __new__(cls):
        self = super().__new__(cls)
        InsaneClass._alive.append(self)

        return weakref.proxy(self)

    def commit_suicide(self):
        self._alive.remove(self)

instance = InsaneClass()
instance.commit_suicide()
print(instance)

# Raises Error: ReferenceError: weakly-referenced object no longer exists

When the object is created in the __new__ method, the instance is replaced by a weak reference proxy and the only strong reference is kept in the _alive class attribute.

What is a weak-reference?

Weak-reference is a reference which does not count as a reference when the garbage collector collects the object. Consider this example:

>>> class Test(): pass

>>> a = Test()
>>> b = Test()

>>> c = a
>>> d = weakref.proxy(b)
>>> d
 
# The weak reference points to the Test() object

>>> del a
>>> c
<__main__.Test object at 0x10670f390> # c still exists

>>> del b
>>> d
 
# d is now only a weak-reference to None. The Test() instance was garbage-collected

So the only strong reference to the instance is stored in the _alive class attribute. And when the commit_suicide() method removes the reference the instance is garbage-collected.