Describe Python garbage collection in Python.
Jul 03, 2025 am 02:07 AMPython's garbage collection mechanism automatically manages memory through reference counting and periodic garbage collection. Its core method is reference counting, which immediately releases memory when the number of references of an object is zero; but it cannot handle circular references, so a garbage collection module (gc) is introduced to detect and clean the loop. Garbage collection is usually triggered when the reference count decreases during program operation, the allocation and release difference exceeds the threshold, or when gc.collect() is called manually. Users can turn off automatic recycling through gc.disable(), manually execute gc.collect(), and adjust thresholds to achieve control through gc.set_threshold(). Not all objects participate in loop recycling. For example, objects that do not contain references are processed by reference counting. Built-in types such as int and string do not participate in loop recycling, and classes that define __del__ methods may affect recycling behavior.
Python handles memory management automatically, and a big part of that is garbage collection. The main idea is that Python keeps track of which objects are still in use and cleans up the ones that aren't — freeing up memory without you having to do it manually.

How Python's Garbage Collector Works
At its core, Python uses reference counting as the primary method. Every object has a count of how many references point to it. When that count drops to zero, the memory is immediately freed.

But reference counting alone can't catch everything — especially circular references , where two or more objects refer to each other but are otherwise unreachable.
For those cases, Python also includes a garbage collector module (gc) that runs periodically to detect and clean up these cycles.

When Does Garbage Collection Happen?
Garbage collection usually happens behind the scenes. Here's when it kicks in:
- During normal program execution, when reference counts drop.
- When the number of allocations minus deallocations exceeds a threshold — this triggers the cyclic garbage collector.
- You can also trigger it manually using
gc.collect()
if needed.
This automatic behavior works well for most applications, but in performance-sensitive or long-running programs, understanding when GC runs can help avoid unexpected pauses.
Controlling Garbage Collection
If you're working with large data structures or need more control over memory cleanup, Python lets you tweak the garbage collector via the gc
module.
Some common things you might do:
- Turn off automatic collection:
gc.disable()
- Run a manual collection:
gc.collect()
- Adjust thresholds:
gc.set_threshold()
This level of control is useful in things like game loops, real-time systems, or services where timing consistency matters.
What Gets Collected (and What Doesn't)
Not all objects are treated the same during garbage collection. For example:
- Objects that don't contain references to other objects may be handled purely by reference counting.
- Objects involved in circular references (like lists containing themselves) are tracked by the garbage collector.
- Some built-in types (like ints or strings) don't participate in cyclic GC because they can't form cycles.
Also, if your class defines __del__
, it can affect how objects are collected — sometimes delaying or complicating the process.
Basically, Python's garbage collection system does most of the heavy lifting for you, but knowing how it works helps you write better-performing and memory-efficient code.
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