Python garbage collector

Question

Given the code sample below, what is the life cycle for bb in in example 1 and for self.bb in example 2

Example 1

import B

class A:
    def __init__( self ):
        bb = B( self )

Example 2

import B

class A:

    def __init__( self ):
        self.bb = B( self )

Edit:

B is another class and for some reason i found it was not garbage collected in the first example. I looked more carefully in my code and i found out B class created a new class C and gave a ref to one of its methods to that C class. In the end C instantiated a loop back thread to wait for events hence B class instance was still alive even though A class init was done.

Thanks all for your answers.

Neither `bb` has **any** lifetime, since you are not creating instances of class A. `bb` in the first example is a local; like all locals it is cleaned up the moment `A.__init__` exits. Your question is rather broad and answered in the Python documentation and elsewhere on Stack Overflow though; what research have you done yourself and what wasn't clear? — Martijn Pieters, Jan 28 '15 at 08:20

Paulo Scardine · Accepted Answer · 2015-01-28T10:31:07.913

0

On both cases there will be no reference to the B instance until you instantiate A.

Once you instantiate A, in the first case it will be discarded right after __init__ runs because bb will be out of scope and there will be no reference left to that B instance, so it will be garbage-collected on the next GC cycle (exactly when is an implementation detail). On the second case, the reference to that B instance will exist as long as a reference for the A instance exists or until you manually remove it.

edited Jan 28 '15 at 10:31

answered Jan 28 '15 at 08:20

Paulo Scardine

73,447
11
124
153

2

In CPython, objects go away the moment their reference count drops to 0. The GC only deals with *circular references*, which doesn't apply here. So the object is reaped *instantly*, not in the next GC cycle. But Jython, IronPython and PyPy are free to use different strategies, and do so. – Martijn Pieters Jan 28 '15 at 08:25
@MartijnPieters This comment you made saved my day. Thanks!!! – George Florea Jan 28 '15 at 08:32
And in Jython, say, there is no guarantee that the garbage is *ever* collected. – Antti Haapala -- Слава Україні Jan 28 '15 at 08:35

Vivek Sable · Answer 2 · 2015-01-28T08:27:23.910

0

In first example bb is local variable for function __init__ The bb variable can access within the same __init__ function.

In 2nd example self.bb is Instance variables for every class object.

edited Jan 28 '15 at 08:27

answered Jan 28 '15 at 08:21

Vivek Sable

9,938
3
40
56

score -2 · Answer 3 · edited May 23 '17 at 12:28

-2

They has not any life-time. You have to inherited.

Example 1

import B
class A:
    def __init__( self ):
        B.__init__(self)
bb = B()

Example 2

import B
class A:
    def __init__( self ):
        B.__init__(self)

bb = B()

For more information about init

edited May 23 '17 at 12:28

Community

1
1

answered Jan 28 '15 at 08:28

sakirecayyok

29
4

Python garbage collector

3 Answers3