# Python3 venv Virtual Environment Fundamentals

__Python Virtual Environments__ are a tool used to create isolated spaces on your computer where you can install 
and manage different versions of Python, as well as their respective packages, without affecting 
the global system installation. This isolation helps avoid version conflicts between projects that 
require different dependencies or libraries. 

Here's an in-depth look at how they work:

### Why Use Virtual Environments?

- Isolation: Each virtual environment is independent of others, ensuring no interference occurs between projects with conflicting requirements.
- Dependency Management: It allows you to manage dependencies for a specific project without affecting other projects or the system's Python installation.
- Reproducibility: By using virtual environments, it becomes easier to replicate your development environment on another machine or share with others.
- Safety: It prevents accidental modification of global packages and allows you to experiment without risking the system's Python installation.

## Create a venv
To create a virtual environment, go to the root of your project and run

``python -m venv venv``

It will create a virtual environment called venv

## Activate venv
`./venv/bin/activate` or `./.venv/bin/activate`

Verify it is working with:

`which python` and it should be `"something-something"/venv/bin/python`



## Intall packages

Depending on what you're gonna do with the project. Use `pip` to install packages.

``pip install jupyter matplotlib numpy pandas scipy scikit-learn``

``pip install Flask``

``pip install django``

or

``python -m pip install -U jupyter matplotlib numpy pandas scipy scikit-learn``

## Create requirements.txt
``pip freeze > requirements.txt``

## Deactivate venv
``deactivate``

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

Place the ``requirements.txt`` file in the root of your project directory. 
When ready to install the dependencies, ensure your terminal is navigated to the project directory 
and your virtual environment is activated. Then, run ``pip install -r requirements.txt`` 
to install the listed packages within your virtual environment.

```bash
python -m venv venv
./venv/bin/activate
pip install -r requirements.txt
```

__Also, more often lately (2023+), people have been suggesting your use `.venv` (note the dot).__
Besure your `.gitignore` file has both `venv/` and `.venv/` in it.