🏠 Virtual Environments

A virtual environment is an isolated Python installation that keeps project dependencies separate from other projects and the system Python.

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✅ Why Virtual Environments?

Without virtual environments: - Project A needs requests==2.25.0 - Project B needs requests==2.28.0 - Conflict! Only one version can be installed globally.

With virtual environments: - Each project has its own isolated site-packages - No conflicts between projects - Reproducible installations

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✅ Creating a Virtual Environment

# Using the built-in venv module (recommended)
python -m venv myenv

# Creates a directory structure:
# myenv/
# ├── bin/           (or Scripts/ on Windows)
# ├── include/
# ├── lib/
# └── pyvenv.cfg

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✅ Activating and Deactivating

# Linux/macOS
source myenv/bin/activate

# Windows (PowerShell)
myenv\Scripts\Activate.ps1

# Windows (CMD)
myenv\Scripts\activate.bat

# Deactivate (any platform)
deactivate

When activated: - python points to the venv's Python - pip install installs to the venv's site-packages - Your prompt usually shows (myenv) prefix

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✅ Checking Your Environment

# See which Python is active
which python        # Linux/macOS
where python        # Windows

# Check the environment
python -c "import sys; print(sys.prefix)"

# List installed packages
pip list

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✅ Project Workflow

# 1. Create venv in project folder
cd myproject
python -m venv .venv

# 2. Activate it
source .venv/bin/activate  # or Windows equivalent

# 3. Install dependencies
pip install requests flask

# 4. Save dependencies
pip freeze > requirements.txt

# 5. Work on your project
python app.py

# 6. Deactivate when done
deactivate

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✅ Common Conventions

• Name: .venv or venv (dot prefix hides it on Unix)
• Location: Inside the project directory
• Git: Add .venv/ to .gitignore (don't commit it!)
• Always use a venv per project

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✅ Alternatives to venv

Tool	Description
venv	Built-in, simple, recommended for most cases
virtualenv	Third-party, more features, faster
conda	Full environment manager, great for data science
pyenv	Manages multiple Python versions
poetry	Modern dependency + venv management

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🔍 Key Takeaways

• Always use virtual environments for Python projects.
• python -m venv .venv creates an isolated environment.
• Activate before installing packages, deactivate when done.
• Add .venv/ to .gitignore.

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