Python - Garbage Collection

Garbage Collection (GC) is the process of automatically destroying objects that are no longer required by the program.

Python provides a built-in Garbage Collector that automatically manages memory.

The programmer does not need to manually free memory as in some other programming languages.

Whenever an object becomes unused and no reference variables point to it, Python's Garbage Collector destroys the object and releases the occupied memory.

• Automatically frees unused memory.
• Improves application performance.
• Prevents memory leaks.
• Removes objects that are no longer required.
• Allows programmers to focus on application logic instead of memory management.

An object becomes eligible for Garbage Collection when its reference count becomes zero.

This means that no reference variable is pointing to the object.

Once the object becomes unreachable, Python's Garbage Collector destroys it automatically.

Reference Count	Object Status
Greater than 0	Object is Active
0	Eligible for Garbage Collection

A Destructor is a special method that is automatically executed just before an object is destroyed.

In Python, the destructor method is represented by __del__().

The main purpose of a destructor is to perform cleanup activities before an object is removed from memory, such as:

• Closing files.
• Closing database connections.
• Releasing network resources.
• Freeing external resources.

Three reference variables point to the same object, so its reference count is 3.

Deleting t1 reduces the count to 2, and deleting t2 reduces it to 1. The object is still alive because t3 continues to reference it.

When t3 is deleted, the reference count becomes zero. The object becomes eligible for garbage collection and the destructor executes automatically before the object is destroyed.

Reference Counting is the mechanism used by Python to keep track of how many reference variables are pointing to an object.

Whenever an object is created, Python maintains a count of all references pointing to that object. This count is called the Reference Count.

The Garbage Collector uses the reference count to determine whether an object is still in use. If the reference count becomes zero, the object becomes eligible for Garbage Collection.

• Creating a new reference increases the count.
• Deleting a reference decreases the count.
• When the count becomes zero, Python destroys the object.

The reference count changes automatically during program execution.

Operation	Reference Count	Object Status
Create Object	1	Alive
Create t2	2	Alive
Create t3	3	Alive
del t1	2	Alive
del t2	1	Alive
del t3	0	Garbage Collection

Python provides the sys.getrefcount() function to display the current reference count of an object.

5

Although only four user-created reference variables exist, the output is 5.

This happens because Python internally maintains one additional temporary reference while calling getrefcount().

Reference	Count
t1	1
t2	1
t3	1
t4	1
Internal Python Reference	1
Total	5

Three reference variables point to the same object.

Deleting t1 and t2 does not destroy the object because t3 still references it.

Only after t3 is deleted does the reference count reach zero, the destructor executes, and the object is destroyed.

The list stores references to three different Test objects.

When del list is executed, the only references to all three objects are removed.

Each object now has a reference count of zero, so the destructor executes once for every object.

Feature	Garbage Collection	Destructor
Purpose	Release Memory	Cleanup Resources
Executed By	Python Garbage Collector	Python Automatically
When Executed	Reference Count Becomes Zero	Just Before Object Destruction
User Invocation	No	No
Main Work	Destroy Object	Close Files, Release Resources