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How to Set Up Python 3, venv, and Virtual Environments

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By SunilKPatro
3 min read
How to Set Up Python 3, venv, and Virtual Environments

Isolating your Python projects prevents dependency conflicts and keeps your global operating system clean. This guide covers how to install Python 3, create a virtual environment (venv), use package files, configure Git, and activate it across different operating systems.

1. Install Python 3

Before creating environments, ensure you have the correct Python 3 version installed.

macOS

Install via Homebrew:

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brew install python

Linux (Ubuntu/Debian)

Update your package manager and install Python 3 along with the required venv package:

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sudo apt update
sudo apt install python3 python3-venv python3-pip -y

Windows

  1. Download the installer from the official Python website.
  2. Run the installer.
  3. Crucial: Check the box that says “Add python.exe to PATH” before clicking Install.

2. Understanding venv: Built-in or Executable?

A common question is whether venv is a separate executable file.

  • It is a built-in module: venv is not a standalone executable or a third-party software tool. It is part of the Python Standard Library bundled directly with Python 3.3 and higher.
  • How it works: When you execute the creation command, Python calls this built-in internal module to generate a standalone directory structure with its own isolated binaries and local site-packages folder.
  • Linux Exception: On some Linux distributions (like Ubuntu), the OS packagers strip the library to save space. You must explicitly run sudo apt install python3-venv to enable it.

3. Create the Virtual Environment

Navigate to your project directory and run the built-in venv module. This creates a localized folder (typically named .venv) containing a copy of the Python executable.

  • macOS / Linux:
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    python3 -m venv .venv
  • Windows:
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    python -m venv .venv

4. Activate the Environment

You must activate the environment in your terminal window before installing packages or running scripts.

macOS & Linux (Bash/Zsh)

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source .venv/bin/activate

Windows (PowerShell)

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.\.venv\Scripts\Activate.ps1

(If you get a script execution error, run Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope Process first).

Windows (Command Prompt)

.venv\Scripts\activate.bat

Verification

Once activated, your terminal prompt will display a visual prefix:

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(.venv) user@computer:~/my-project\$

5. Manage Project Packages with requirements.txt

In production and collaborative workflows, dependencies are saved inside a requirements.txt file instead of committing the entire environment folder to GitHub.

Create and Edit requirements.txt Explicitly

You do not have to wait until packages are installed to create this file. You can manually create a file named requirements.txt in your root folder and type out your packages explicitly using various version structures:

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# Install the latest compatible version
requests

# Pin to an exact, specific version
flask==3.0.2

# Accept any version greater than or equal to a specific release
numpy>=1.26.0

# Prevent breaking updates but allow patches
pandas~=2.2.0

Install Packages From a requirements.txt File

Once you have written or added packages to this file explicitly, activate your environment and run the following to install all listed dependencies at once:

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pip install -r requirements.txt

Save Current State Automatically

Alternatively, if you installed packages manually and want to freeze your current project packages into a text file automatically:

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pip freeze > requirements.txt

6. Configure Git with a .gitignore File

You should never commit your .venv directory to GitHub. It contains thousands of source files specific to your operating system architecture, which bloats your repository and breaks for developers on different operating systems.

Create a file named .gitignore in your root project directory and add the following lines to exclude your environment files:

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# Byte-compiled / optimized / DLL files
__pycache__/
*.py[cod]
*\$py.class

# Virtual Environments
.venv/
venv/
ENV/
env/

# IDE files (Optional but recommended)
.vscode/
.idea/

7. Leave the Environment

To exit the virtual environment and return to your system’s global Python context, simply run:

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deactivate
PYTHON
setupInstall python
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