Why Use Virtual Environments?

1. Dependency Isolation: Each project has its own packages
2. Version Control: Different projects can use different package versions
3. Clean System: Keeps your system Python installation clean
4. Reproducibility: Easy to recreate project environments
5. No Conflicts: Avoids package version conflicts

Creating a Virtual Environment

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python -m venv myenv

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pip install virtualenv
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virtualenv myenv

Activating a Virtual Environment

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myenv\Scripts\activate

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source myenv/bin/activate

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(myenv) C:\Users\YourName>

Deactivating a Virtual Environment

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deactivate

Working with Virtual Environments

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# Activate first
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source myenv/bin/activate  # Linux/Mac
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# or
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myenv\Scripts\activate     # Windows
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# Then install packages
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pip install requests
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pip install numpy

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pip list

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pip freeze > requirements.txt

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pip install -r requirements.txt

Virtual Environment Best Practices

1. One per project: Create a separate virtual environment for each project
2. Name clearly: Use descriptive names like project_name_env
3. Add to .gitignore: Don’t commit virtual environments to git
4. Document dependencies: Always maintain requirements.txt
5. Recreate when needed: If environment gets corrupted, recreate it

Project Structure with Virtual Environment

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my_project/
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    .gitignore          # Excludes venv/
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    requirements.txt
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    README.md
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    venv/               # Virtual environment (not committed)
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    src/
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        my_code.py
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    tests/
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        test_code.py

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# Virtual environments
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venv/
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env/
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ENV/
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.venv
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# Python cache
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__pycache__/
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*.pyc
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*.pyo
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*.pyd
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# Requirements
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# Keep requirements.txt, ignore others

Recreating a Virtual Environment

If you need to recreate an environment:

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# Remove old environment
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rm -rf myenv  # Linux/Mac
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rmdir /s myenv  # Windows
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# Create new environment
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python -m venv myenv
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# Activate
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source myenv/bin/activate  # Linux/Mac
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myenv\Scripts\activate      # Windows
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# Install dependencies
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pip install -r requirements.txt

Virtual Environment Tools

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python -m venv myenv

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pip install virtualenv
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virtualenv myenv

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conda create -n myenv python=3.9
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conda activate myenv

Common Workflow

1. Create project directory

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   mkdir my_project
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   cd my_project
   

2. Create virtual environment

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   python -m venv venv
   

3. Activate virtual environment

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   source venv/bin/activate  # Linux/Mac
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   venv\Scripts\activate     # Windows
   

4. Install packages

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   pip install package_name
   

5. Create requirements.txt

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   pip freeze > requirements.txt
   

6. Work on project

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   python my_script.py
   

7. Deactivate when done

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   deactivate
   

Troubleshooting

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python --version
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which python  # Linux/Mac
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where python  # Windows

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which python  # Should show venv path

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chmod +x myenv/bin/activate

Exercises

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commands = """1. python -m venv myenv
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2a. myenv\\Scripts\\activate (Windows)
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2b. source myenv/bin/activate (Linux/Mac)
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3. pip install requests
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4. deactivate"""
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print(commands)

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print("Create: pip freeze > requirements.txt")
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print("Install: pip install -r requirements.txt")