Giving Virtualenv Verisimilitude

While learning Flask, one of my biggest challenges has been wrapping my head around how virtualenv works. This blog post is really just to lay out my basic understanding of how it works. One of my main sources of information has come from this fantastic blog post by Jamie Matthews.

Here’s some of the more important points that needs to be understood before understanding virtualenv:

• pip is a tool that installs packages from the Python Package Index (aka PyPI; the Cheeseshop).
  • PyPI is an online repository with over 60,000 packages included in it. Whenever you use pip to install a package, it gets the package from here.
• pip, by default, installs packages to Python’s site-packages directory. Anything installed in Python’s site-packages directory can be imported by any of your programs.
• virtualenv creates a complete copy of everything needed to run a Python program, including a copy of the python binary itself, a copy of the entire Python standard library, a copy of the pip installer, and (crucially) a copy of the site-packages directory

How do you install virtualenv?

• For Windows: make sure that your Path is set to access commands from your Python directory, or alternatively, just navigate to your Python directory.
• Run pip install virtualenv

How do you setup an environment?

• Change your directory into the root of your project directory, and then use the virtualenv command-line tool to create a new environment:
  • virtualenv venv
  • The env part is just the name of the directory you want to store the environment in. You can change venv to anything, but it is standard practice to keep it named venv
  • One of the folders created by virtualenv is called Scripts. Some scripts are created in this folder when you first created your environment. Of note are the activate and deactivate scripts. Run these to activate and deactivate your environment.
  • Cool note: you need to specify the path when you run activate (by entering something like: c:\myProject\env\Scripts\activate) but you don’t need to specify the path when you run deactivate – running activate makes the association for you. Convenient!

Here are some other resources on basic virtualenv functionality:

• I got a lot of cool hints from this StackOverflow page.
• This official documentation page on virtualenv

And if you are interested in virtualenv with PythonAnywhere, these threads might help as well:

• Reddit Thread
• PythonAnywhere Forum Thread