Python Destructors

What is a Destructor?

A destructor is a special method in Python that is automatically called when an object is destroyed.

Purpose of Destructor

Destructor is used to perform cleanup work, such as:

• Freeing up memory
• Releasing external resources
• Closing files or database connections

Method Name: __del__(self)

It has a fixed name __del__ and is automatically executed. It accepts no arguments except self.

Constructor vs Destructor

Understanding the difference between the creation and destruction phases of an object.

Implementation Examples

1. Simple Creation and Destruction

class Demo:
    def __init__(self):
        print("Object created")

    def __del__(self):
        print("Object destroyed")

d = Demo()
# Output:
# Object created
# Object destroyed (when program ends)

2. Using the 'del' Keyword

You can force a destructor to run by explicitly deleting the object reference.

class Sample:
    def __init__(self):
        print("Created")
    def __del__(self):
        print("Destroyed")

s = Sample()
del s # Explicitly triggers __del__

3. Interaction with Normal Methods

class Test:
    def __init__(self):
        print("Constructor")
    def show(self):
        print("Normal method")
    def __del__(self):
        print("Destructor")

t = Test()
t.show()

Object Life Cycle

The journey of an object from start to finish in Python memory.

• Step 1: Object Created (__init__ called)
• Step 2: Object Used (Normal methods called)
• Step 3: Object Destroyed (__del__ called)

Garbage Collection

Python’s automatic memory management system (Garbage Collector) removes objects when their reference count hits 0, triggering the destructor.

Important Rules & Real-Life Usage

Rules to Follow:

• Only one destructor allowed per class.
• Execution time is not always guaranteed immediately (depends on GC).
• Should only contain cleanup logic, not critical program logic.

Real-Life Example: File Handling

class FileHandler:
    def __init__(self):
        self.f = open("test.txt", "w")
        print("File opened")

    def __del__(self):
        self.f.close()
        print("File closed safely")

Quick Revision Summary

Exam One-Liners:

• Definition: A special method automatically called to free resources when an object is destroyed.
• Memory Trick: Created → __init__ | Used → methods | Destroyed → __del__