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

File: gc-example-1.py import gc # create a simple object that links to itself class Node: def _ _init_ _(self, name): self.name = name self.parent = None self.children = [] def addchild(self, node): node.parent = self self.children.append(node) def _ _repr_ _(self): return "" % (repr(self.name), id(self)) # set up a self-referencing structure root = Node("monty") root.addchild(Node("eric")) root.addchild(Node("john")) root.addchild(Node("michael")) # 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.