The gc Module

(Optional, 2.0 and later) The gc module provides an interface to the built-in cyclic garbage collector.

Python uses reference counting to keep track of when to get rid of objects; as soon as the last reference to an object goes away, the object is destroyed.

Starting with Version 2.0, Python also provides a cyclic garbage collector, which runs at regular intervals. This collector looks for data structures that point to themselves, and attempts to break the cycles. Example 1-87 shows this.

You can use the gc.collect function to force full collection. This function returns the number of objects destroyed by the collector.

Example 1-87. Using the gc Module to Collect Cyclic Garbage


import gc

# create a simple object that links to itself
class Node:

 def _ _init_ _(self, name): = name
 self.parent = None
 self.children = []

 def addchild(self, node):
 node.parent = self

 def _ _repr_ _(self):
 return "" % (repr(, id(self))

# set up a self-referencing structure
root = Node("monty")


# remove our only reference
del root

print gc.collect(), "unreachable objects"
print gc.collect(), "unreachable objects"

12 unreachable objects
0 unreachable objects

If you're sure that your program doesn't create any self-referencing data structures, you can use the gc.disable function to disable collection. After calling this function, Python 2.0 works exactly like 1.5.2 and earlier.

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Python Standard Library
Python Standard Library (Nutshell Handbooks) with
ISBN: 0596000960
EAN: 2147483647
Year: 2000
Pages: 252
Authors: Fredrik Lundh © 2008-2020.
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