What is the __del__ method, How to call it?

Question

I am reading a code. There is a class in which __del__ method is defined. I figured out that this method is used to destroy an instance of the class. However, I

Answer 1

The __del__ method (note spelling!) is called when your object is finally destroyed. Technically speaking (in cPython) that is when there are no more references to your object, ie when it goes out of scope.

If you want to delete your object and thus call the __del__ method use

del obj1

which will delete the object (provided there weren't any other references to it).

I suggest you write a small class like this

class T:
    def __del__(self):
        print "deleted"

And investigate in the python interpreter, eg

>>> a = T()
>>> del a
deleted
>>> a = T()
>>> b = a
>>> del b
>>> del a
deleted
>>> def fn():
...     a = T()
...     print "exiting fn"
...
>>> fn()
exiting fn
deleted
>>>   

Note that jython and ironpython have different rules as to exactly when the object is deleted and __del__ is called. It isn't considered good practice to use __del__ though because of this and the fact that the object and its environment may be in an unknown state when it is called. It isn't absolutely guaranteed __del__ will be called either - the interpreter can exit in various ways without deleteting all objects.