Deleting objects

[Terry Reedy]

"Thomas Philips" <tkpmep at hotmail.com> wrote in message
news:b4a8ffb6.0404220608.56bf3d63 at posting.google.com...
> I'm teaching myself OOP using Michael Dawson's "Python Programming For
> The Absolute Beginner" and have a question about deleting objects. My
> game has two classes: Player and Alien, essentially identical,
> instances of which can shoot at each other. Player is described below
>
> class Player(object):
>     #Class attributes for class Player
>     n=0 #n is the number of players
>
>     #Private methods for class Player
>     def __init__(self,name):
> self.name = name

You appear to have use a tab here and spaces below.  Never mix, and stick
with spaces for posted code.

>         self.strength = 100
>         Player.n +=1
>
>     def __del__(self):
>         Player.n -=1
>         print "I guess I lost this battle"
>
>     #Public methods for class Player
>     def blast(self,enemy,energy):
>         enemy.hit(energy)
>
>     def hit(self,energy):
>         self.strength -= energy
>         if(self.strength <= 50):
>             self.__del__()
>
> I instantiate one instance of each class:
> Hero = Player("Me")
> Villain = Alien("Not Me")
>
> If Hero hits Villain with
> Hero.blast(Villain, 100),
>
> Villain dies and executes its destructor (__del__).

However, the name 'Villain' is still bound to the corresponding object in
globals().  Executing the __del__ method of an object does *NOT* delete the
object.  This *only* thing special about that method is that it is called
'behind the scenes' when an objects refcount goes to 0.

> The game then
> ends. However, when I execute the program in IDLE, IT FINISHES BY
> EXECUTING THE DESTRUCTOR FOR BOTH HERO AND VILLAIN.

__del__ methods are not destructors.  There are merely called be the
interpreter's internal destructor function.

> How can this be? As one of the two objects was destroyed prior to the
> end of the game,

As explained above, it was not destroyed.  You merely called a method that
happened to be named __del__.

Getting rid of *all* references to an object, in order to allow destruction
(but not guarantee it), can be difficult.

> how can it be re-destroyed when the program ends?

Terry J. Reedy