lang-python

# AI Skill: Python Engineering (Python 3 Specialist) This skill guides the AI to act as a specialist in the **Python 3** language, aligned strictly with the guidelines of the official language documentation ([docs.python.org/pt-br/3](https://docs.python.org/pt-br/3/)), the Language Reference, the Standard Library Reference, and the Python Enhancement Proposals (PEPs). The goal is to build idiomatic, expressive, maintainable, safe, and high-performance code. --- ## 🧭 General Guidelines and Language Fundamentals (docs.python.org) While working under this skill, apply the official Python Software Foundation principles strictly: ### 1. Philosophy and Idiomatic Style (PEP 20, PEP 8 & PEP 257) - **The Zen of Python (PEP 20)**: - *Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex.* - Avoid unreadable code tricks ("code golf") in favor of clarity and maintainability. - **PEP 8 Style Guide**: - Naming: `snake_case` for variables, functions, and methods; `PascalCase` for classes; `ALL_CAPS` for constants. - Strict 4-space indentation (never mix tabs and spaces). - Import organization at the top of the file, split into 3 blocks: (1) Standard Library, (2) Third-Party Libraries, and (3) Local Modules. - **Docstring Conventions (PEP 257)**: - Write explanatory docstrings for modules, classes, and public functions using the triple-quote convention `"""Explanatory text."""`. ### 2. Language Data Model (Data Model & Dunder Methods) - **Special Methods (__dunder__)**: Implement the Pythonic behavior of your custom classes using the official Data Model: - Representation: `__str__` (for user-friendly display) and `__repr__` (for unambiguous debugging). - Context Managers: `__enter__` and `__exit__` (synchronous) or `__aenter__` and `__aexit__` (asynchronous with `async with`). - Collections and Iteration: `__len__`, `__getitem__`, `__setitem__`, `__iter__`, `__next__`. - Comparison and Hashing: `__eq__` and `__hash__` for objects usable as dictionary and set keys. ### 3. Structural Pattern Matching (PEP 634/635/636) - Use the `match / case` statement (Python 3.10+) to destructure sequences, dictionaries, and class instances cleanly: ```python from dataclasses import dataclass @dataclass(slots=True) class Point: x: float y: float def process_event(event: tuple | Point) -> str: match event: case Point(x=0, y=0): return "Center origin" case Point(x=x, y=y) if x == y: return f"Point on the main diagonal: {x}" case ("click", x, y): return f"Pointer click: ({x}, {y})" case ("key", str(k)) if len(k) == 1: return f"Key pressed: {k}" case _: return "Unknown event" ``` ### 4. Static Typing System and Generics (PEP 484, PEP 526 & PEP 695) - **Type Annotations (`typing`)**: Apply type hints to function signatures and core domain attributes. - **Modern Generic Syntax (Python 3.12+ - PEP 695)**: - Declare generics directly with the `type` keyword and bracketed parameters: ```python # PEP 695 syntax (Python 3.12+) type Result[T] = dict[str, T] class Repository[T]: def __init__(self, initial_data: list[T]) -> None: self._items: list[T] = initial_data def get_first(self) -> T | None: return self._items[0] if self._items else None ``` --- ## 🛠️ Standard Library Highlights (Python Standard Library) When implementing solutions, prioritize the language's mature built-in modules before adding external dependencies: - **Object Orientation and Data**: - `dataclasses`: Creating data classes with `dataclass(slots=True, frozen=True)`. - `enum`: Defining strongly typed enums (`Enum`, `IntEnum`, `StrEnum`). - `collections`: `defaultdict`, `Counter`, `deque`, `namedtuple`. - **I/O and File System**: - `pathlib`: Object-oriented file path manipulation (`Path(__file__).parent`). - `contextlib`: Simplified context manager creation with `@contextmanager`. - `json`: Safe JSON serialization and parsing. - **Asynchronous Execution and Concurrency**: - `asyncio`: Native event loop, coroutines (`async def`), tasks (`asyncio.create_task`), and semaphores (`asyncio.Semaphore`). - `concurrent.futures`: Parallel processing based on threads (`ThreadPoolExecutor`) or processes (`ProcessPoolExecutor`). - **Operation and Debugging**: - `logging`: Structured logging configured per module (`logging.getLogger(__name__)`). - `unittest`: Native unit test suite (for compatibility without external packages). --- ## 🧰 Recommended Code Patterns ### 1. Custom Context Manager (`contextlib`) ```python from contextlib import contextmanager from typing import Generator import time import logging logger = logging.getLogger(__name__) @contextmanager def execution_timer(task_name: str) -> Generator[None, None, None]: start_time = time.perf_counter() try: yield finally: elapsed = time.perf_counter() - start_time logger.info(f"Task '{task_name}' completed in {elapsed:.4f}s") ``` ### 2. Native Asyncio Application with Signal Handling ```python import asyncio import logging logging.basicConfig(level=logging.INFO) logger = logging.getLogger("worker") async def worker_task(task_id: int, semaphore: asyncio.Semaphore) -> None: async with semaphore: logger.info(f"Starting task {task_id}") await asyncio.sleep(0.5) logger.info(f"Completed task {task_id}") async fn main() -> None: semaphore = asyncio.Semaphore(3) tasks = [asyncio.create_task(worker_task(i, semaphore)) for i in range(10)] await asyncio.gather(*tasks) if __name__ == "__main__": asyncio.run(main()) ``` --- ## ⚙️ Modern Environment Management and Packaging (PEP 621) - **`pyproject.toml`**: Centralize project metadata, dependencies, and tool configuration (`pytest`, `black`, `mypy`, `ruff`) in a single file per PEP 621. - **Virtual Environments (`venv`)**: Isolate dependencies using the native module `python -m venv .venv` or modern high-performance managers such as `uv` or `poetry`. --- ## 🔒 Security Issues and Safe Practices - **Insecure Deserialization (CWE-502)**: Never deserialize untrusted data using `pickle`, `marshal`, or `shelve`. When using PyYAML, always force the call through `yaml.safe_load()`. - **Command and Code Injection**: Avoid using `eval()`, `exec()`, and `subprocess.Popen(..., shell=True)` with user-supplied data. Use the object-oriented API with argument lists. - **Mutable Default Arguments**: Avoid defining lists or dictionaries as default arguments in functions (e.g., `def func(val=[])`), because they persist across calls and can cause logic bugs and data leakage. - **Path Traversal (CWE-22)**: Use `pathlib.Path` and validate resolved path safety against base paths with `Path.resolve()` (e.g., preventing navigation to parent folders via `../`). ## 🔗 Integration with Other Skills - To create parameterized unit and integration test suites in Python, see [framework-pytest](../../frameworks/framework-testing-python/SKILL.md) and [framework-unittest](../../frameworks/framework-testing-python/SKILL.md). - To integrate and optimize relational and NoSQL database access in Python (SQLAlchemy, psycopg, PyMongo, Tortoise ORM), see [dba-database-administrator](../../roles/dba-database-administrator/SKILL.md), [db-postgresql](../../data/db-postgresql/SKILL.md), [db-sqlite](../../data/db-sqlite/SKILL.md), [db-mariadb](../../data/db-mariadb/SKILL.md), and [db-mongodb](../../data/db-mongodb/SKILL.md). - To develop offensive tools, network scripts, and security utilities in Python, see [pentest-scripter-python-bash-go](../../security/appsec/pentest-scripter-python-bash-go/SKILL.md). - To audit Python code against security flaws (SAST) and apply clean-code fixes, see [sast-code-review](../../security/appsec/sast-code-review/SKILL.md) and [clean-code-reusability](../../engineering/practices/clean-code-reusability/SKILL.md).