Modern tooling
uv, ruff, pyproject.toml, packaging, and current Python project workflows.
How to Bind and Mock structlog Context in Python
Shows how to bind persistent key-value context to a structlog logger, unbind keys, and mock the logger in tests to verify context is passed correctly.
import structlog
from unittest.mock import patch
logger = structlog.get_logger()
def demo():
logger = structlog.get_logger()
logger = logger.bind(user_id=42, request_id="abc123")
logger.info("user logged in", action="login")
# Unbind a key
logger = logger.unbind("user_id")
logger.info("r…How to Build a Chainable Filter Helper in Python
A beginner-friendly dataclass helper that chains filters, uniqueness, and slicing on any sequence, returning a plain list at the end.
from dataclasses import dataclass
from typing import Callable, Iterator, Sequence, TypeVar
T = TypeVar("T")
@dataclass
class FilterAssistant:
"""Beginner-friendly helper to filter any collection."""
data: Sequence[T]
def where(self, predicate: Callable[[T], bool]) -> "FilterAssistant":
return …How to Build a Wheel with Hatchling in Python
Build a Python wheel using the hatchling build backend and the build package, handling missing project metadata automatically.
import subprocess
import sys
import tempfile
from pathlib import Path
def build_wheel_with_hatchling(project_dir: str) -> str:
"""Build a wheel using hatchling and return the wheel file path."""
project_path = Path(project_dir)
# Simulate a minimal project structure if missing
if not (project_path /…How to Create Interactive CLI Prompts in Python with questionary
Build mock interactive command-line prompts using questionary's select and text widgets with graceful handling of user cancellation.
import questionary
def main():
# Mock interactive prompts using questionary's select and text
choice = questionary.select(
"What is your favorite programming language?",
choices=["Python", "JavaScript", "Go", "Rust"]
).ask()
# ask() returns None if user cancels; handle gracefully
…How to Create a Mock Virtualenv with an Activation Script in Python
Create a mock virtualenv directory with a generated bash activation script using Python's standard library.
import os
import subprocess
import sys
from pathlib import Path
def mock_virtualenv(name: str = "myenv") -> Path:
"""Create a mock virtualenv directory and activation script."""
env_dir = Path(name)
env_dir.mkdir(exist_ok=True)
(env_dir / "bin").mkdir(exist_ok=True)
activate_script = f"""#!/bin/…How to Create a Rich Console Progress Bar Mock in Python
This code uses Rich's Console and Progress API to build a simulated progress bar for a long-running task, updating progress and printing status messages.
import time
from rich.console import Console
from rich.progress import Progress, BarColumn, TextColumn, PercentageColumn
console = Console()
def run_simulation():
console.print("[bold cyan]Starting simulated task...[/bold cyan]")
with Progress(
TextColumn("[bold blue]{task.description}[/bold blu…How to Define Nox Sessions in Python
Automate repetitive tasks like testing and linting with reusable Nox sessions.
import nox
@nox.session(python=["3.9", "3.10"])
def tests(session):
session.install("pytest")
session.run("pytest")
@nox.session(python="3.9")
def lint(session):
session.install("ruff")
session.run("ruff", "check", ".")
if __name__ == "__main__":
print("Nox sessions defined: tests, lint")
…How to Enforce Indentation Rules From .editorconfig in Python
A mock function that reads .editorconfig-style indentation rules (spaces or tabs, size) and fixes indentation in source code lines by tracking brace depth.
def enforce_indent(editorconfig_rules, file_content):
"""
Mock function to enforce indentation rules from .editorconfig.
Returns the content with indentation fixed (or unchanged if already compliant).
"""
indent_style = editorconfig_rules.get("indent_style", "spaces")
indent_size = int(editorco…How to Export a Conda Environment YAML File in Python
Generate a mock conda environment YAML export with a reusable Python function and the PyYAML library.
import yaml
def conda_env_mock(name="demo_env", channels=None, packages=None):
channels = channels or ["defaults"]
packages = packages or [
"python=3.11",
"pip",
"numpy=1.24.3",
"pandas=2.0.3",
]
env_dict = {
"name": name,
"channels": channels,
…How to Format Data with Python's datetime and JSON Helpers
A beginner-friendly set of helper functions to format dates and safely read/write JSON files in Python.
from datetime import datetime
from pathlib import Path
import json
def format_today(pattern: str = "%Y-%m-%d") -> str:
"""Return today's date formatted with the given pattern."""
return datetime.now().strftime(pattern)
def load_json(file_path: str) -> dict:
"""Read and parse a JSON file safely."""
…How to Generate a Mock Rollbar Error Report in Python
Create a realistic fake Rollbar error report with random timestamps, levels, messages, and counts for testing and demos.
import json
import random
import time
from datetime import datetime, timedelta
def mock_rollbar_report(n_errors=5):
messages = [
"TypeError: unsupported operand type(s) for +: 'int' and 'str'",
"KeyError: 'user_id'",
"ValueError: invalid literal for int() with base 10: 'abc'",
"At…How to Generate a Mock devcontainer.json Config in Python
Build a reproducible devcontainer.json file with Python, composing name, image, extensions, forwarded ports, and a post-create command as a dict.
import json
from pathlib import Path
def create_devcontainer_config(
image: str = "mcr.microsoft.com/devcontainers/python:3.11",
name: str = "python-dev-container",
ports: list[int] | None = None,
post_create: str | None = None,
) -> dict:
config = {
"name": name,
"image": image,
…How to Initialize Sentry SDK with a Mock DSN in Python
Initialize the Sentry SDK in Python with a mock DSN to test error tracking without sending real events, then verify the DSN configuration.
import sentry_sdk
# Initialize Sentry SDK with a mock DSN (no real events will be sent)
sentry_sdk.init(
dsn="https://mock-public@mock-host/mock-project",
traces_sample_rate=1.0,
environment="development",
)
# Capture a test message to confirm SDK is configured
sentry_sdk.capture_message("Test message fr…How to List Pre-commit Hooks from YAML Config in Python
Parse a .pre-commit-config.yaml file with PyYAML and print every hook ID paired with its source repository.
import yaml
pre_commit_config = """
repos:
- repo: https://github.com/pre-commit/pre-commit-hooks
rev: v4.5.0
hooks:
- id: trailing-whitespace
- id: end-of-file-fixer
- id: check-yaml
- repo: https://github.com/psf/black
rev: 23.11.0
hooks:
- id: black
"""
def list_hooks(c…How to Load and Inspect CSV Data with a Dataclass Helper in Python
This code defines a DataHelper dataclass that reads a CSV file into a list of dictionaries and prints basic dataset information.
from pathlib import Path
from dataclasses import dataclass
from typing import Any
@dataclass
class DataHelper:
"""Simple helper for loading and inspecting CSV data."""
filepath: Path
def load_csv(self, *, delimiter: str = ",") -> list[dict[str, Any]]:
"""Read CSV into a list of dictionaries."""
…How to Load and Inspect Data Files in Python
A beginner-friendly DataLoader dataclass that loads JSON or text files and provides methods to preview and inspect the data.
from dataclasses import dataclass, field
from pathlib import Path
import json
from typing import Any, Dict, List
@dataclass
class DataLoader:
"""Simple helper to load and inspect data files for beginners."""
path: Path
data: Any = field(init=False, default=None)
def __post_init__(self) -> None:
…How to Load and Save CSV and JSON Files in Python
A beginner-friendly data helper that loads or saves CSV and JSON files using only the Python standard library, with automatic format detection from the file extension.
from pathlib import Path
import json
import csv
def load_data(file_path):
"""Load CSV or JSON data from disk based on file extension."""
path = Path(file_path)
if path.suffix == ".json":
with path.open() as f:
return json.load(f)
elif path.suffix == ".csv":
with path.open(…How to Load envrc Files in Python
Parse and apply direnv-style envrc files to the current environment, with proper handling of variables, comments, and quotes.
import os
import tempfile
from pathlib import Path
from unittest.mock import patch
def load_envrc(envrc_path):
"""Parse an envrc-style file and apply it to the current environment."""
env_changes = {}
with open(envrc_path, "r") as f:
for line in f:
line = line.strip()
if l…How to Mock BugSnag Notify in Python
Use unittest.mock to simulate BugSnag notifications, verify calls, and test error handling without external dependencies.
import mock
bugsnag = mock.MagicMock()
def notify_error(message, severity="error"):
bugsnag.notify(message, severity=severity)
if __name__ == "__main__":
notify_error("Test error", severity="warning")
bugsnag.notify.assert_called_once_with("Test error", severity="warning")
print("Mocked BugSnag noti…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 Click CLI App Subcommands in Python
Simulate Click-style CLI subcommand calls in Python by using argparse with subparsers and mocking sys.argv in tests or scripts.
import sys
import argparse
def do_greet(args):
print(f"Hello, {args.name}!")
def do_goodbye(args):
print(f"Goodbye, {args.name}!")
def main():
parser = argparse.ArgumentParser(prog="clickapp")
subparsers = parser.add_subparsers(dest="command", required=True)
greet_parser = subparsers.add_par…How to Mock Commitizen Version Bump in Python
Simulate commitizen's version bump logic and mock the subprocess call to avoid real execution in tests.
import subprocess
from unittest.mock import patch, MagicMock
def bump_version(current_version: str, increment: str = "patch") -> str:
"""Simulate commitizen's version bump logic."""
major, minor, patch = map(int, current_version.split("."))
if increment == "major":
major += 1
minor = 0
…How to Mock Fabric Connections in Python for Task Testing
Create a lightweight MockConnection class to replace fabric.Connection and test task functions without SSH.
from fabric import Connection
class MockConnection:
"""Minimal mock of fabric.Connection for task testing."""
def __init__(self):
self.commands = []
def run(self, command, **kwargs):
self.commands.append(command)
return f"OK: {command}"
def deploy(conn):
"""Deploy the app:…How to Mock OpenTelemetry Tracer Setup in Python
Set up a mock OpenTelemetry tracer with an in-memory span exporter to capture spans for testing and debugging.
from opentelemetry import trace
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import SimpleSpanProcessor
from opentelemetry.sdk.trace.export.in_memory_span_exporter import InMemorySpanExporter
def setup_tracer():
provider = TracerProvider()
exporter = InMemorySpanExpo…Browse by section
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