Environment Variables

Environment Variables

A computer's variables are stored on a local computer, and thus can be controlled and secured locally.

Used here, a computer environment is a general term meaning the configuration settings that a computer, or computer session, use to adjust its behavior. Your environment may specify where programs are located in your filesystem, which programs may take precedence over others, and passwords used to access secured systems. Your computer may maintain many settings (such as Windows' Registry), but among them are environment variables, which are specific key/value pairs that specify some of these settings. These variables are stored on your individual computer or the computer you are working with. You may maintain environment variables that apply to all users of your system, or just to you.

Retrieving Environment Variables through Python

We can use os.getenv() or os.environ to retrieve environment variables.

In each of these examples, MY_PASSWORD is a sample environment variable key.

import os

# dynamically retrieve key/value pair from environment
val = os.getenv('MY_PASSWORD')

# equivalent, uses a dict that contains all key/value pairs
val = os.environ['MY_PASSWORD']

Setting Environment Variables on Your Computer

The specific steps will depend on your platform and OS Version.

Windows (Note that if these instructions don't work for your version of Windows, you can find many tutorials, including screenshots, online.)

• Right-click the Windows icon and select System
• In the Settings window, under Related Settings, click Advanced system settings
• On the Advanced tab, click Environment Variables
• There are two sets of variables: System (applies to all users) and User (applies only to your work)
• Click New to create a new environment variable
• Click Edit to edit an existing environment variable

Mac/Linux

• Open the Terminal program. A white window with black text appears.
• Determine which shell type you are using (the "shell" is the program we interact with in a Terminal session).
  • look closely at the text prompt
  • if the prompt ends with a '$', you are using the "bash" shell and will edit the .bash_profile file
  • if the prompt ends with a '%' you are most likely using a "zsh" shell and will edit the .zshrc shell
  • there is also a possibility that you will be running a different shell type; consult your system or sysadmin
• Display "hidden" files in your home directory
  • On the Mac, open a Finder window to your Home directory (click the Home icon if needed) and press Cmd Shift . (period)
  • On Linux, open a file browser window to your Home directory (click the Home icon if needed) and press Ctrl-H
  • Hidden files (starting with a period) should be displayed, usually in a grey color
• Create or edit the file you identified above
  • If the file you identified above (.bash_profile or .zshrc does not exist, create one - copy an existing file and rename it
  • Edit the file to add or change environment variables. A good general approach to updating an environment variable is the following entry:
    
    

    export MY_VAR='value':$MY_VAR
    

    
    

    where 'MY_VAR' is the key and 'value' is the value

  • You can also find more specific instructions for updating Mac or Linux environment variables online
  • Please keep in mind that in order for any changes to take effect, you must open a new terminal window