Environment variables are accessed through os.environ:

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

To see a list of all environment variables:

print(os.environ)

If a key is not present, attempting to access it will raise a KeyError. To avoid this:

# Returns `None` if key doesn't exist
print(os.environ.get('KEY_THAT_MIGHT_EXIST'))

# Returns `default_value` if key doesn't exist
print(os.environ.get('KEY_THAT_MIGHT_EXIST', default_value))

# Returns `default_value` if key doesn't exist
print(os.getenv('KEY_THAT_MIGHT_EXIST', default_value))