Basic15 min read
File I/O & Modules
Read and write files safely and organize code into modules and packages.
Reading and Writing Files
open(path, mode, encoding="utf-8") returns file objects. Use with statements for automatic close even on exceptions.
Text mode handles encoding/decoding; binary mode reads bytes for images and PDFs. pathlib.Path offers ergonomic path operations cross-platform.
For large files, iterate line by line instead of read() entire content into memory.
- Always specify encoding for text files on Windows
- Use tempfile for sensitive scratch files
- Check path.exists() before optional reads
from pathlib import Path
config = Path("config.toml").read_text(encoding="utf-8")
Path("out.json").write_text(json.dumps(data), encoding="utf-8")Modules and Packages
Each .py file is a module; folders with __init__.py are packages. import loads modules once into sys.modules cache.
Relative imports work inside packages: from .models import User. Absolute imports from project root are clearer in apps.
__all__ lists public API names for from package import * though explicit imports are preferred.
- Avoid circular imports by extracting shared interfaces
- Use pyproject.toml for modern package metadata
- Run python -m package.module for correct sys.path
# myapp/services/users.py
from myapp.models import User
def get_user(user_id: int) -> User:
...