memory_management

Memory Management

CPython uses reference counting plus a cyclic garbage collector for circular references.

Files

File	Description
example.py	Refcount, cyclic GC, weakref

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Descriptive Example

Scenario

Understand when objects are freed and how weak references observe without preventing collection.

import sys, weakref, gc

obj = ["hello", "world"]
print(sys.getrefcount(obj) - 1)   # adjust for getrefcount's own reference

ref = obj                         # refcount +1
alias = obj                       # refcount +1

del ref, alias, obj               # refcount → 0 → object freed

# Weak reference — doesn't prevent collection
data = ["important"]
weak = weakref.ref(data)
print(weak() is not None)   # True
del data
print(weak() is None)       # True — object collected

Cyclic references

a = []
b = []
a.append(b)
b.append(a)
del a, b
gc.collect()    # cycle detector frees both

Reference counting alone can't free cycles — the cyclic GC handles them.

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Interview Q&A

Q1: How does Python manage memory?
A: Primary: reference counting (increment on assign, decrement on del/scope exit; free at zero). Secondary: cyclic GC for circular references.

Q2: Can Python have memory leaks?
A: Yes — global references, closures capturing large objects, C extensions, or cycles with __del__ methods that prevent GC collection.

Q3: What is weakref?
A: Reference that doesn't increment refcount. Useful for caches and observers — object can be collected when no strong refs remain.

Q4: Is __del__ reliable for cleanup?
A: No. Call order is undefined, may not run at interpreter shutdown, and can resurrect objects. Prefer context managers and try/finally.

Q5: What is gc.collect()?
A: Forces a full garbage collection cycle. Useful after deleting large cyclic structures. Usually not needed in normal code.

Q6: Python vs Java GC?
A: Python: refcount (deterministic, immediate) + cycle detector. Java: tracing GC (generational). Python has no manual free() — developer doesn't manage memory directly.

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Run

python3 example.py