reference - How to give object away to python garbage collection?

Question

There are several threads on Python garbage collection in SO, and after reading about five, plus some doc on line, i am still not sure as to how garbage collection works and how i should manage objects which i am not using. In fact somewhere i read one should not do anything about collecting garbage, others tell one should del objects, while others again explain de-referencing an object is enough for Python to collect it as garbage.

So, at the risk of creating a duplicate, i will ask the question again, but differently, hoping to get more comprehensive and clearer information.

In my case i want to make a small simulation with objects representing people. Several instances of the Person() class will be created. It should exist for some time until it virtually "dies" while other instances will be created.

Now how do i make this Person() instance "die" (assuming many many of these instances will be created and i don't want these instances to hang out like ghosts)?

There are several ways i can reference an object:

john = Person('john')

or

people = []
people.append(Person('john'))

or

people = {}
people['john'] = Person('john')

What is the best way to keep my program clean, freeing resources optimally? And what is the best way then to reference my object so i can control the deletion of the object?

Answer 1

Maybe this also can help:

>>> # Create a simple object with a verbose __del__ to track gc.
>>> class C:
...     def __del__(self):
...         print "delete object"
... 
>>> c = C()
>>> # Delete the object c successfully.
>>> del c
delete object
>>> # Deletion of an object when it go out of the scope where it was defined.
>>> def f():
...     c = C()
...
>>> f()
delete object
>>> c = C()
>>> # Create another reference of the object.
>>> b = c
>>> # The object wasn't destructed the call of del only decremented the object reference. 
>>> del c
>>> # Now the reference counter of the object reach 0 so the __del__ was called. 
>>> del b
delete object
>>> # Create now a list that hold all the objects.
>>> l = [C(), C()]
>>> del l
delete object
delete object
>>> # Create an object that have a cyclic reference.
>>> class C:
...     def __init__(self):
...         self.x = self
...     def __del__(self):
...         print "delete object"
... 
>>> c = C()
>>> # Run the garbage collector to collect object.
>>> gc.collect()
9
>>> # the gc.garbage contain object that the gc found unreachable and could not be freed.  
>>> gc.garbage
[<__main__.C instance at 0x7ff588d84368>]
>>> # Break the cyclic reference.
>>> c.x = None
>>> # And now we can collect this object.
>>> del c
delete object
>>> # Create another object with cyclic reference.
>>> c = C()
>>> # When closing the interactive python interpreter the object will be collected.
delete object

Refrences : del method ; gc module ; weakref module