How to access environment variable values

Question

I set an environment variable that I want to access in my Python application. How do I get its value?

Answer 1

Environment variables are accessed through os.environ

import os print(os.environ['HOME']) 

Or you can see a list of all the environment variables using:

os.environ 

As sometimes you might need to see a complete list!

# using get will return `None` if a key is not present rather than raise a `KeyError` print(os.environ.get('KEY_THAT_MIGHT_EXIST'))  # os.getenv is equivalent, and can also give a default value instead of `None` print(os.getenv('KEY_THAT_MIGHT_EXIST', default_value)) 

The Python default installation location on Windows is C:\Python. If you want to find out while running python you can do:

import sys print(sys.prefix) 

Answer 2

To check if the key exists (returns True or False)

'HOME' in os.environ 

You can also use get() when printing the key; useful if you want to use a default.

print(os.environ.get('HOME', '/home/username/')) 

where /home/username/ is the default