Dependency Management + pipenv

Dependency management in Python refers to the process of identifying, installing, and managing the external libraries and packages that a project relies upon. This is crucial for several reasons: project isolation (preventing conflicts between different projects' dependencies), reproducibility (ensuring that a project can be run with the exact same dependencies across different environments), and avoiding 'dependency hell' (issues arising from conflicting versions of shared dependencies).

Historically, Python developers used `pip` for package installation and `virtualenv` (or `venv` built-in) for creating isolated environments. While effective, this often required manual management of `requirements.txt` files and separate commands for environment activation and package installation.

`pipenv` emerges as a higher-level tool that aims to simplify and unify this process. It combines the best aspects of `pip` and `virtualenv` into a single, intuitive workflow. `pipenv` automatically creates and manages a virtual environment for your project, handles package installation and uninstallation, and provides robust dependency resolution and locking.

Key features and benefits of `pipenv`:
1. Automatic Virtual Environments: When you start a `pipenv` project, it automatically creates a virtual environment if one doesn't exist, isolating your project's dependencies from other Python projects.
2. `Pipfile` and `Pipfile.lock`: Instead of `requirements.txt`, `pipenv` uses `Pipfile` to declare your project's direct dependencies (similar to `package.json` in Node.js or `Gemfile` in Ruby). It then generates `Pipfile.lock`, which pins the -exact- versions of all direct and transitive dependencies, ensuring reproducible builds across machines.
3. Simplified Workflow: Commands like `pipenv install <package>` handle both virtual environment creation/activation and package installation.
4. Development Dependencies: `pipenv install --dev <package>` allows you to manage development-specific dependencies separately, which won't be installed in production environments by default.
5. Graph and Security Checks: `pipenv graph` visualizes your dependency tree, and `pipenv check` performs security audits against known vulnerabilities.
6. Environment Management: `pipenv shell` activates the project's virtual environment, and `pipenv run <command>` executes a command within the virtual environment without explicitly activating it.
7. Deterministic Builds: `Pipfile.lock` ensures that `pipenv install` will always install the exact same set of dependencies, making deployments and team collaboration much smoother.

By abstracting away much of the manual work involved in `pip` and `virtualenv`, `pipenv` streamlines Python project setup, development, and deployment, making dependency management more robust and less error-prone.

 First, ensure pipenv is installed globally:
 pip install --user pipenv

 1. Start a new project directory
mkdir my_pipenv_project
cd my_pipenv_project

 2. Initialize pipenv for the project (creates Pipfile)
 If a virtual environment doesn't exist for this project, pipenv will create one automatically.
pipenv --python 3.9   You can specify a Python version, or it will use default
echo "--- Pipfile created ---"
cat Pipfile

 3. Install a dependency (e.g., requests)
 This will install 'requests' into the virtual environment and update Pipfile and Pipfile.lock.
pipenv install requests
echo "\n--- Pipfile after requests install ---"
cat Pipfile
echo "\n--- Pipfile.lock after requests install (first few lines) ---"
head -n 20 Pipfile.lock

 4. Create a simple Python script to use the dependency
echo 'import requests\n\nresponse = requests.get("https://www.google.com")\nprint(f"Status Code: {response.status_code}")' > main.py

 5. Run the script using pipenv run (executes within the virtual environment)
echo "\n--- Running script via pipenv run ---"
pipenv run python main.py

 6. Activate the virtual environment shell
echo "\n--- Entering pipenv shell ---"
pipenv shell
 Inside the shell, you can run python commands directly
 (e.g., python main.py, pip list)
 Example of running a command inside the activated shell
python main.py
pip list | grep requests
exit  Exit the virtual environment shell
echo "--- Exited pipenv shell ---"

 7. Install a development dependency (e.g., pytest)
 This adds pytest to the [dev-packages] section of Pipfile.
pipenv install pytest --dev
echo "\n--- Pipfile after pytest install ---"
cat Pipfile

 8. Uninstall a dependency
pipenv uninstall requests
echo "\n--- Pipfile after requests uninstall ---"
cat Pipfile
echo "\n--- Pipfile.lock after requests uninstall (first few lines) ---"
head -n 20 Pipfile.lock

 9. View the dependency graph
echo "\n--- Dependency graph ---"
pipenv graph

 10. Clean up (remove virtual environment and project files)
 Use with caution! This removes the virtual environment.
pipenv --rm
cd ..
rm -rf my_pipenv_project