Computer Vision Project - Nix Development Environment

This project uses Nix Flakes to provide a reproducible development environment with Python and virtual environment support.

Prerequisites

1. Install Nix (if not already installed):

   curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install

2. Enable Nix Flakes (if not already enabled):

   • The Determinate Nix installer enables flakes by default
   • If using the official Nix installer, add to ~/.config/nix/nix.conf:

     experimental-features = nix-command flakes
     

Getting Started

1. Enter the Nix Development Shell

nix develop

This will automatically:

• Download and set up Python 3.11
• Create a Python virtual environment (.venv) if it doesn't exist
• Activate the virtual environment
• Display helpful instructions

2. Install Dependencies

Option A: From requirements.txt

pip install -r requirements.txt

Option B: Install packages individually

pip install opencv-python numpy pillow

Option C: Install deep learning frameworks

# For PyTorch
pip install torch torchvision

# For TensorFlow
pip install tensorflow

Project Structure

.
├── flake.nix          # Nix flake configuration
├── .gitignore         # Git ignore patterns
├── requirements.txt   # Python dependencies
├── README.md          # This file
└── .venv/            # Python virtual environment (created by you)

Common Workflows

Daily Development

# Enter Nix shell (automatically creates and activates venv)
nix develop

# Work on your project...
# The virtual environment is already activated!

# Exit when done (this also deactivates the venv)
exit

Installing New Packages

# The venv is already activated when you run 'nix develop'
# Just install packages directly:
pip install <package-name>

# Update requirements.txt
pip freeze > requirements.txt

Updating Dependencies

# Update all packages
pip install --upgrade -r requirements.txt

# Update specific package
pip install --upgrade <package-name>

Customizing the Environment

Adding System Packages

Edit flake.nix and add packages to the buildInputs list:

buildInputs = with pkgs; [
  python311
  python311Packages.pip
  # Add more packages here
  ffmpeg
  imagemagick
];

Changing Python Version

In flake.nix, replace python311 with your desired version:

• python39 for Python 3.9
• python310 for Python 3.10
• python312 for Python 3.12

Troubleshooting

"command not found: nix"

• Make sure Nix is installed and your shell has been restarted

"error: experimental Nix feature 'flakes' is disabled"

• Enable flakes in your Nix configuration (see Prerequisites)

Virtual environment not activating automatically

• The Nix shell automatically creates and activates the venv
• If you see issues, try deleting .venv and run nix develop again
• Check that the shellHook in flake.nix is properly configured

Import errors after installing packages

• Ensure the virtual environment is activated
• Verify the package is installed: pip list

Tips

• The virtual environment is automatically activated when you run nix develop
• Keep requirements.txt updated for reproducibility
• Use pip freeze > requirements.txt to capture exact versions
• The .gitignore file excludes the .venv directory from Git

Next Steps

1. Create your Python scripts in the project directory
2. Import your dependencies
3. Build your computer vision project!

Happy coding! 🚀