02_setup.md

Goals

• Understand the importance of virtual environments
• Install and create a virtual environment
• Install and use virtualenvwrapper
• Install Flask through pip

Virtual Environments

A virtual environment is a self-contained directory tree that contains a Python installation for a particular version of Python, plus a number of additional packages. It is used to isolate a particular project to avoid conflicts with the requirements of another project. virtualenv is a tool used to create Python virtual environments.

Installing 'virtualenv'

Check if virtualenv already exists in your system through your terminal or console:

$ virtualenv --version

If you see a version number, that means you already have it installed and may now proceed to the next step. Otherwise, install virtualenv through the Python package manager, a.k.a. pip:

$ pip install virtualenv

Visit this link for more info on how to make sure you have the latest version of pip installed.

Working with 'virtualenv'

To create a virtual environment, go to your project's directory and run virtualenv:

cd path/to/directory
virtualenv env

The second argument refers to the location where you want to create the virtualenv. Generally, you can just create this in your project and call it env. virtualenv will create a virtual Python installation in the env folder.

Note: Don't forget to exclude your virtualenv directory from your version control system using .gitignore or similar.

To activate your virtualenv:

Windows
$ .\env\Scripts\activate

Linux and macOS
$ source env/bin/activate

To confirm if you're in the virtualenv by checking the location of your Python interpreter, which should point to the env directory:

Windows
$ where python

Linux and macOS
$ which python

As long as your virtualenv is activated, pip will install packages into that specific environment and you'll be able to import and use packages in your Python application.

To leave your virtualenv, simply run:

$ deactivate

Bonus: virtualenvwrapper

To make working with virtual environments easier (especially for Windows uers), you can use virtualenvwrapper, which is a set of extensions to the virtualenv tool. It also places all of your virtual environments in a single location.

Mac:
$ pip install virtualenvwrapper
$ export WORKON_HOME=~/Envs
$ source /usr/local/bin/virtualenvwrapper.sh

Windows:
$ pip install virtualenvwrapper-win

Once you've installed virtualenvwrapper, create a new isolated development environment:

mkvirtualenv portfolio

This produced a folder named portolio inside the Envs folder with a clean copy of Python inside.

To activate virtualenv with virtualenvwrapper:

$ workon portfolio

You may also check the list of existing virtual environments in your Envs folder by typing:

$ workon

Installing Flask

To install flask through pip, just run:

$ pip install flask

Saving packages

To save the list of packages installed in your environment for easier reproduction:

$ pip freeze > requirements.txt

This will save what you've installed so far in a text file named requirements.txt.

To install the packages listed in a requirements.txt file:

$ pip install -r requirements.txt