Modern tooling
uv, ruff, pyproject.toml, packaging, and current Python project workflows.
How to Mock CLI Output in Typer with unittest.mock
Mock and capture Typer CLI output using unittest.mock.patch and io.StringIO for testing command-line applications.
import typer
from unittest.mock import patch
import io
app = typer.Typer()
@app.command()
def greet(name: str, age: int = 18, uppercase: bool = False):
"""Greet a person with optional formatting."""
message = f"Hello {name}, age {age}"
if uppercase:
message = message.upper()
typer.echo(messag…How to Mock subprocess.run for Black Formatter in Python
Use unittest.mock to simulate subprocess.run calls in a Python function that runs the Black formatter, allowing isolated testing without executing external commands.
import subprocess
from unittest.mock import Mock, patch
def run_black_formatter(file_path: str, check_only: bool = False) -> dict:
"""Run black formatter on a file via subprocess."""
cmd = ["black", "--check" if check_only else "-", file_path]
result = subprocess.run(cmd, capture_output=True, text=True)
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Modern tooling — Python code examples
What you will find here
This page collects modern tooling snippets — short, copy-ready Python you can paste into our free online IDE and run without installing anything. Each sample includes a plain-English explanation and the full source code.
Samples vs tutorials and challenges
Samples are quick reference — one concept per page. For step-by-step teaching, use our Python tutorials. To test yourself, try quizzes or coding challenges. Clean up style with the Python formatter.