README.md

Structs and Classes (Python)

This module introduces object modeling with dataclass-style structures and classes.

Learning Metadata

• Difficulty: Intermediate.
• Estimated Time: 35-50 minutes.
• Prerequisites: 01-foundations/functions, 01-foundations/scope-and-lifetime-basics.
• Cross-Language Lens: Compare lightweight records, full classes, and method receivers to see how each language models data plus behavior.

Quick Run

python example/main.py

Topics Covered

• Lightweight value modeling with @dataclass.
• Stateful behavior using classes and private-by-convention fields.
• Constructor guards to preserve valid object state.
• Method-based updates for controlled mutations.

Common Pitfalls

• Placing mutable shared defaults directly on class definitions.
• Letting invalid constructor inputs propagate through the object lifecycle.
• Updating internal state from outside helper methods.

Exercise Focus

• exercises/01.py: model a rectangle using a class with methods.
• exercises/02.py: build an encapsulated Counter class with commands.

Exercise Specs

1. exercises/01.py

• Input: width and height.
• Output: area and perimeter.
• Edge cases: non-positive dimensions should stop with a message; decimal values should work.

2. exercises/02.py

• Input: sequence of commands (inc, dec, reset, stop).
• Output: counter value updates and final value.
• Edge cases: unknown commands; immediate stop.

Checkpoint

• I can explain when @dataclass is enough and when a class with methods is better.
• I can enforce simple invariants in constructors.
• I can keep state updates inside well-named methods.
• I completed exercises/01.py.
• I completed exercises/02.py.