Modern tooling

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 …

14 0 Open

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.

devcontainer json config

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,
…

14 0 Open

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.

pre-commit yaml pyyaml

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…

pytest parametrize testing

How to Parametrize Tests in Python with pytest

This code demonstrates how to use pytest's @pytest.mark.parametrize decorator to run a single test function against multiple input sets, ensuring comprehensive coverage with minimal code duplication.

import pytest


def multiply(a, b):
    return a * b


@pytest.mark.parametrize("x, y, expected", [
    (2, 3, 6),
    (4, 5, 20),
    (0, 10, 0),
    (7, 1, 7),
])
def test_multiply(x, y, expected):
    result = multiply(x, y)
    assert result == expected, f"multiply({x}, {y}) = {result}, expected {expected}"


if _…

pyright type-checking mocking

How to Type Check a Mock with pyright in Python

Shows how pyright validates a mock function against a TypedDict and Callable signature before runtime.

from typing import TypedDict, Callable


class User(TypedDict):
    id: int
    name: str


def get_user_name(user_id: int, get_user: Callable[[int], User]) -> str:
    user = get_user(user_id)
    return user["name"]


def mock_get_user(user_id: int) -> User:
    return {"id": user_id, "name": f"User {user_id}"}


if…

How to Use pytest Fixtures and conftest.py for Shared Setup in Python

Learn how to define reusable pytest fixtures for shared setup and use them to keep tests clean and maintainable.

pytest fixtures conftest

import pytest

class Calculator:
    def add(self, a, b):
        return a + b

    def multiply(self, a, b):
        return a * b


@pytest.fixture
def calc():
    return Calculator()


@pytest.fixture
def sample_numbers():
    return (3, 5)


def test_add(calc, sample_numbers):
    a, b = sample_numbers
    assert c…

13 0 Open

validation dictionary helper

How to Validate Data with a Simple Dict-Based Rules Helper in Python

Validates a dictionary against a set of callable rules, printing pass/fail per field and returning an overall boolean.

import json
from pathlib import Path
from typing import Any, Callable


def validate_data(
    data: dict[str, Any],
    rules: dict[str, Callable[[Any], bool]],
    path: Path | None = None,
) -> bool:
    """Validate a dict against a set of simple rules."""
    all_valid = True
    for field, validator in rules.item…