Modern tooling

from datetime import datetime
from pathlib import Path
import json

def to_json(data, indent=2):
    """Convert Python data to pretty-printed JSON string."""
    return json.dumps(data, indent=indent, default=str)

def from_json(json_string):
    """Parse JSON string back into Python data."""
    return json.loads(jso…

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.

conda yaml environment

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,
        …

17 0 Open

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.

datetime json files

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 Mock Fabric Connections in Python for Task Testing

Create a lightweight MockConnection class to replace fabric.Connection and test task functions without SSH.

fabric mocking testing

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:…

14 0 Open

How to Mock Twine Upload to TestPyPI in Python

Simulate a twine upload to TestPyPI with a dry-run mock function that validates distribution files and prints the intended upload action without any network call.

twine testpypi mock

import subprocess
import sys

# Mock twine upload to TestPyPI using subprocess dry-run
def mock_twine_upload(dist_file: str, repo_url: str = "https://test.pypi.org/legacy/") -> None:
    """Simulate twine upload by checking dist file and printing intended action."""
    if not dist_file.endswith((".whl", ".tar.gz")):
…

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 _…

15 0 Open

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…

15 0 Open

pip-tools requirements mock

Mock pip-compile to Resolve Requirements in Python

A mock function that mimics pip-compile by converting a requirements.in file into pinned, locked package versions.

import subprocess
import tempfile
from pathlib import Path


def compile_requirements_mock(requirements_in: str) -> str:
    """Mock pip-compile: resolve a simple requirements.in into a locked format."""
    lines = [line.strip() for line in requirements_in.splitlines() if line.strip() and not line.startswith("#")]
  …