python-development

Python Development Patterns

Modern Python (3.10+) best practices for web development, data science, and general programming.

CRITICAL: Agentic-First Python Development

Pre-Development Verification (MANDATORY)

Before writing ANY Python code:

1. CHECK PYTHON INSTALLATION
   → run_terminal_cmd("python3 --version")
   → run_terminal_cmd("pip --version")
   → run_terminal_cmd("uv --version")  # Modern package manager
   
2. VERIFY CURRENT VERSIONS (use web_search)
   → web_search("Python stable version December 2024")
   → web_search("FastAPI latest version 2024")
   → web_search("Django LTS version 2024")
   
3. CHECK EXISTING PROJECT
   → Does pyproject.toml/requirements.txt exist? Read it first!
   → Is there a virtual environment?
   → What dependencies are already installed?
   
4. VIRTUAL ENVIRONMENT (ALWAYS USE)
   → run_terminal_cmd("python3 -m venv .venv")
   → run_terminal_cmd("source .venv/bin/activate")

CLI-First Python Development

ALWAYS use CLI for package management:

# Virtual environment (ALWAYS create first)
python3 -m venv .venv
source .venv/bin/activate  # Unix
.venv\Scripts\activate  # Windows

# Modern: uv (10-100x faster than pip)
uv venv
uv pip install fastapi uvicorn
uv pip sync requirements.txt

# Traditional: pip
pip install fastapi uvicorn
pip install -r requirements.txt
pip freeze > requirements.txt

# Framework CLIs (use these for scaffolding)
# Django
django-admin startproject myproject
python manage.py startapp myapp

# FastAPI with cookiecutter
pip install cookiecutter
cookiecutter https://github.com/tiangolo/full-stack-fastapi-template

# Poetry (if project uses it)
poetry init
poetry add fastapi
poetry install

Post-Edit Verification

After ANY Python code changes:

# Type checking
mypy src/

# Linting
ruff check .
ruff format --check .

# Or older tools
flake8 .
black --check .

# Tests
pytest
pytest --cov=src

# Verify imports work
python -c "import mypackage"

Common Python Syntax Traps (Avoid These!)