🐍 Python Environment Setup: A Complete Guide to venv and pipenv (with Pytest Testing)

Setting up a proper Python environment is crucial for writing clean, testable, and maintainable code — whether you’re building a simple script or a full-scale data science pipeline.

In this article, I’ll break down how to manage your Python environments using two tools: venv (Python’s built-in virtual environment tool) and pipenv (a higher-level tool for dependency management). You’ll also learn how to test your code with pytest.
🔹 Why Use a Virtual Environment?
A virtual environment isolates your project’s dependencies from your global Python installation. This prevents conflicts and keeps your project clean and reproducible.
🟩 Option 1: Using venv (Built-in)
🔧 Step-by-Step Setup
Create the environment

`python -m venv env
Activate it`

On Windows:

env\Scripts\activate

On macOS/Linux:

source env/bin/activate

Install packages

pip install requests

Install pytest for testing

pip install pytest

Freeze dependencies

pip freeze > requirements.txt

Deactivate when done
✅ Example Test with pytest
calculator.py

def add(a, b):
    return a + b

test_calculator.py

from calculator import add

def test_add():
    assert add(2, 3) == 5

Run your tests with:

pytest

🟦 Option 2: Using pipenv (Modern and Streamlined)
pipenv simplifies dependency management and keeps everything tracked in Pipfile.

🔧 Step-by-Step Setup
Install pipenv

pip install pipenv

Create an environment and install a package

pipenv install requests

Install pytest as a dev dependency

pipenv install --dev pytest

Activate the shell

pipenv shell

Run your tests

pytest

Exit the shell

exit

🧪 Why Use pytest?
Clean syntax with simple assert statements

Fast test discovery

Plugins for coverage, mocking, fixtures, etc.
📁 Suggested Folder Structure

my_project/
├── env/ or .venv/         # virtual environment (excluded from Git)
├── calculator.py
├── test_calculator.py
├── requirements.txt or Pipfile
└── .gitignore

Add this to .gitignore:

env/
.venv/
__pycache__/
.pytest_cache/