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Smart Pointers in Depth (Python)

This module adapts smart pointer ideas to Python references, ownership slots, and weakref.

Learning Metadata

Difficulty: Advanced.
Estimated Time: 45-60 minutes.
Prerequisites: 04-expert/memory-management-and-raii.
Cross-Language Lens: Compare explicit ownership tools in C++ with managed references, pointer conventions, and weak-reference patterns elsewhere.

Quick Run

python example/main.py

Topics Covered

Moving an owned reference by reassigning it and clearing the previous owner.
Using None as an explicit empty ownership slot.
Observing objects without keeping them alive via weakref.ref.
Distinguishing strong references from weak observers.

Common Pitfalls

Assuming a weak reference behaves like a normal strong reference.
Forgetting to clear the old owner after a transfer.
Dereferencing optional references without checking for None.
Keeping accidental strong references in caches or observers.

Cross-Language Notes

Python treats references as the default, so this module compares C++ smart pointers with aliasing, cloning, and weakref.
Compared with C++, ownership is far less encoded in syntax and much more about disciplined object relationships.
The main teaching goal is to notice when sharing is intentional and when it is accidental.

Exercise Focus

exercises/01.py: move an owned note between holders.
exercises/02.py: observe cache entries through weakref.ref.

Exercise Specs

exercises/01.py

Input: none.
Output: ownership transfer logs before and after moving.
Edge cases: moving from an empty holder; destination already occupied.

exercises/02.py

Input: none.
Output: alive/expired cache lookup logs.
Edge cases: expired weak reference; cache miss.

Checkpoint

I can explain strong vs weak references in Python.
I can model ownership transfer with reassignment and None.
I can choose when a weak observer is appropriate.
I completed exercises/01.py.
I completed exercises/02.py.