Python Virtual Environments — Never Mess Up Your System Python

Why Virtual Environments?

Virtual environments create isolated Python environments for each project. Without them, different projects requiring different package versions would conflict.

Creating a Virtual Environment

# Standard library venv
python3 -m venv myproject-env

# Activate it
source myproject-env/bin/activate  # macOS/Linux
myproject-env\Scripts\activate     # Windows

# Install packages — they stay isolated
pip install requests flask

# Deactivate when done
deactivate

Managing Dependencies

# Save current dependencies
pip freeze > requirements.txt

# Install from requirements.txt
pip install -r requirements.txt

Using Poetry (Recommended)

# Create new project
poetry new my-project
cd my-project

# Add dependencies
poetry add requests
poetry add --group dev pytest black

# Install all dependencies
poetry install

Best Practices

• Always use virtual environments — never install globally
• Add venv/ to .gitignore
• Pin versions for reproducibility
• Use Poetry for new projects