How Garbage Collection Works in Python: A Developer’s Guide

If you're writing Python code that deals with objects, lists, or custom classes, you’re already depending on Python’s garbage collection mechanism—even if you don’t know it.

This guide walks you through how garbage collection works in Python, why it's important, and what you can do to work with it—not against it.

🧠 What Is Garbage Collection in Python?

Garbage collection (GC) in Python is the automatic process of reclaiming memory when an object is no longer used. You don’t have to manually free memory, but you should understand how GC behaves to avoid memory leaks and performance issues.

Python uses two primary techniques:

1. Reference Counting (immediate cleanup)
2. Cyclic Garbage Collector (periodic cleanup for reference cycles)

🔄 Step 1: Understanding Reference Counting

Every Python object tracks how many references point to it. When that number hits zero, the object is deleted.

✅ What you need to know:

• Most objects are collected immediately this way
• Functions like del decrease the reference count
• Built-in functions like id() and sys.getrefcount() help you inspect ref counts

♻️ Step 2: Handling Circular References with Cyclic GC

Reference counting fails with circular references, such as:

class Node:
    def __init__(self):
        self.ref = None

n1 = Node()
n2 = Node()
n1.ref = n2
n2.ref = n1

These objects refer to each other and will never reach a reference count of zero.

Python’s cyclic GC scans object graphs periodically to:

• Detect cycles
• Break unreachable ones

You can also trigger GC manually:

import gc
gc.collect()

🧪 Step 3: Checking Garbage Collection in Action

Use the gc module to inspect and debug memory:

import gc
print(gc.get_count())        # View GC thresholds
print(gc.garbage)            # View unreachable objects

You can also disable or tweak GC:

gc.disable()                 # Turn off cyclic GC
gc.set_threshold(100, 5, 5)  # Adjust thresholds

💡 Pro Tips for Developers

• Use __del__ methods with caution — they may delay GC or break it in circular references
• Avoid circular structures unless necessary
• Profile memory with tools like objgraph, tracemalloc, or memory_profiler

🔍 Frequently Asked Questions

What is garbage collection with an example?

It’s the automatic freeing of memory. For example, when a function returns and its local variables are no longer used, GC may clean them up.

Is Python dynamically typed and garbage-collected?

Yes. Python does both — variables are type-checked at runtime and memory is freed automatically.

What’s the difference between del and garbage collection?

del decreases reference count; it doesn’t guarantee object deletion unless the count hits zero. GC may still be required for cycles.

What triggers garbage collection in Python?

The cyclic GC is triggered when allocated object counts exceed a threshold, or you call gc.collect() manually.

📚 Related Guides

• Memory Stack vs Heap in Python →
• Multithreading in Python →

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