Python Cheat Sheet

Python cheat sheet with real commands and snippets for setup, core workflows, debugging, and production-safe automation patterns. If you are working across tools, pair this with the Django Cheat Sheet and FastAPI Cheat Sheet.

Setup and Tooling

Goal: Install and verify language toolchain

# Run python command
python -m venv .venv

# Run source command
source .venv/bin/activate

# Run python command
python -m pip install --upgrade pip

Core Workflows

Goal: Run and build source code

# Execute python workflow
python app.py

# Execute python workflow
python -m module_name

Goal: Use a practical code snippet

# Dataclass model with a derived property
from dataclasses import dataclass

@dataclass
class Item:
    name: str
    price: float

    @property
    def price_cents(self) -> int:
        return int(self.price * 100)

Testing and Formatting

Goal: Run automated tests

# Execute test-related command
pytest

# Execute test-related command
pytest -q

Goal: Run lint and formatter checks

# Execute quality command
ruff check .

# Execute quality command
black .

Automation and CI

Goal: Create a repeatable CI shell step

# Run strict shell mode for CI step
set -euo pipefail

# Install dependencies deterministically
npm ci || pip install -r requirements.txt || true

# Run tests and fail fast on errors
pytest

Debugging and Troubleshooting

Goal: Trace runtime issues

# Print runtime and package manager versions
node --version || python --version || true

# Search stack traces and TODO markers
rg "Traceback|Exception|TODO" .

# Re-run tests with verbose output
pytest -v || pytest --verbose || true

Common Gotchas

• Pin Python language/runtime versions in local and CI environments.
• Keep formatting and linting automated to avoid noisy diffs in code review.
• Prefer explicit dependency lock files for reproducible builds.
• Write small, deterministic tests that can run quickly in pre-commit checks.
• Document compiler/interpreter flags used in production builds.

Related Sheets

• Django Cheat Sheet — daily Django commands and production-ready examples.
• FastAPI Cheat Sheet — daily FastAPI commands and production-ready examples.
• Flask Cheat Sheet — daily Flask commands and production-ready examples.