LLD Lab Stage 1: Sets L0 (Objects from zero) + L1 (The four pillars)

Beginner-first, concept-before-example, Python-only, real-life anchored:

L0 · Objects from zero — what a class is and why OOP exists (the ATM
design vs street machines), self demystified (a.deposit(500) ==
BankAccount.deposit(a, 500)), instance vs class data (LibraryCard and
the shared mutable-attribute bug), identity vs equality (two Rs500
notes; __eq__/__hash__ and the equal->same-shelf law), encapsulation
as invariant-guarding (the teller and the vault), traps + 4-question
interrogation with hint sketches.

L1 · The four pillars — one household story mapping all four,
abstraction as the wall-socket promise (extension test passed in week
one), inheritance + polymorphism (one send() call site, many
notifiers), composition-over-inheritance as the flagship (the 2^n
class explosion vs slots, engine swapped at runtime), enums / value
vs entity / classmethod constructors, UML-lite (the four arrows),
traps + interrogation incl. the penguin problem and Stack(list).

Atlas restructured to the agreed 10-set plan (L0-L9), L0+L1 marked
done. Interactive: 2 step-players (life of an object, engine swap),
6 diagrams, 8 predict-checks, 7 ladder drills, 8 flashcards.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: DeepCodeWork