chapter_11_pythonic_object

Chapter 11 — A Pythonic Object

Theme: To build a class that feels like a native Python object, you must integrate seamlessly with Python's core protocols (formatting, object representation, hashing) and optimize its memory layout.

What You'll Learn

Topic	Key insight
Representations	__repr__ is for debugging (Python expression). __str__ is for display.
Formatting	__format__ enables integration with f-strings and custom format specs.
Hashing	To be hashable, an object must be immutable. Use @property getters without setters.
Alt Constructors	Use @classmethod to create objects from varying input formats (e.g., frombytes).
Name Mangling	__var becomes _Class__var. It prevents accidental subclass overrides, not deliberate hacking.
__slots__	Bypasses the per-instance __dict__, saving significant memory for millions of objects.

Key Files

• examples.py — A practical Vector2d class supporting hashing, formatting, and bytes.
• exercises.py — Custom mini-languages for __format__ and name-mangling tests.
• mini_project.py — An implementation-focused Color class with hex/rgb formatting and __slots__.
• benchmarks.py — Explores memory reduction via __slots__.
• notes.md — Reference on @classmethod vs @staticmethod and representation dunders.
• pitfalls.md — Notes on mutable hash keys and inherited __slots__.
• interview_questions.md — L3 to L6 interview prep.
• architecture_notes.md — How __slots__ works via C-level descriptors.

30-Second Rules

# Rule 1: Always provide a __repr__ that looks like source code
def __repr__(self):
    return f"{type(self).__name__}({self.x!r}, {self.y!r})"

# Rule 2: Use classmethods for alternative constructors
@classmethod
def from_json(cls, data):
    return cls(**json.loads(data))

# Rule 3: Use __slots__ for classes with many simple instances
class Point:
    __slots__ = ('x', 'y')  # Disables __dict__, saving significant memory
    def __init__(self, x, y):
        self.x = x
        self.y = y

Reference: Fluent Python 2nd ed., Chapter 11 — pages 391–430