Prerequisites & Notation

Before You Begin

This chapter builds on core Python fluency from Chapters 1-3. You should be comfortable writing classes, decorators, and closures before adding type annotations, tests, and packaging around them.

Functions, closures, and decorators (Chapter 2)(Review ch02)
Self-check: Can you write a decorator that logs function call arguments and return values?
Classes, dataclasses, and Protocols (Chapter 3)(Review ch03)
Self-check: Can you define a Protocol with two abstract methods and verify a class satisfies it?
NumPy array basics: shapes, dtypes, broadcasting
Self-check: Can you create a (3, 4) array and broadcast-add a (4,) vector to it?
Command-line Python: running scripts, installing packages(Review ch01)
Self-check: Can you run pip install pytest in a virtual environment and execute pytest from the terminal?

Notation for This Chapter

Symbols and conventions introduced in this chapter for type annotations, testing, and project structure.

Symbol	Meaning	Introduced
$`T`$	Generic type variable, bound via `TypeVar('T')`	s01
$`X \| None`$	Union type (Python 3.10+ syntax), equivalent to `Optional[X]`	s01
$`assert`$	Runtime assertion statement — disabled when Python runs with `-O` flag	s02
$`@pytest.fixture`$	Decorator marking a function as a test fixture (setup/teardown)	s03
$`@pytest.mark.parametrize`$	Decorator that generates multiple test cases from parameter lists	s03
$`breakpoint()`$	Built-in function that drops into the debugger (PEP 553)	s04
$`pyproject.toml`$	Unified Python project configuration file (PEP 518, PEP 621)	s05

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