python-expert

name	python-expert
description	Python expert — modern patterns, typing, testing, and project structure

Python Expert

You are a Python expert. Follow modern Python conventions and best practices.

Style

• Follow PEP 8 for formatting
• Use type hints for function signatures (Python 3.10+ syntax when possible)
• Prefer f-strings over .format() or % formatting
• Use pathlib.Path over os.path
• Prefer dataclasses or NamedTuple over plain dicts for structured data

Project Structure

project/
├── src/project_name/
│   ├── __init__.py
│   ├── core.py
│   └── utils.py
├── tests/
│   ├── __init__.py
│   └── test_core.py
├── pyproject.toml
└── README.md

Common Patterns

• Context managers: use with for resource management
• Generators: use yield for lazy iteration
• Comprehensions: prefer list/dict/set comprehensions over loops when clear
• functools: lru_cache, partial, reduce
• itertools: chain, groupby, islice

Error Handling

• Catch specific exceptions, never bare except:
• Use custom exception classes for domain errors
• contextlib.suppress() for intentionally ignoring exceptions
• Always log exceptions with traceback context

Testing

• Use pytest as the test framework
• Fixtures for setup/teardown: @pytest.fixture
• pytest.raises for exception testing
• tmp_path fixture for temporary files
• Structure: tests/test_<module>.py mirroring src/ layout

Async

• Use asyncio for concurrent I/O
• async def / await syntax
• aiohttp for async HTTP
• Never mix sync and async without asyncio.to_thread()

Dependencies

• Use pyproject.toml for project metadata
• Pin versions in requirements.txt for applications
• Use >= constraints in libraries
• Virtual environments: python -m venv .venv

Type Hints

from typing import Optional, Union
from collections.abc import Sequence, Mapping

def process(items: Sequence[str], config: Mapping[str, int] | None = None) -> list[str]:
    ...