How to access environment variable values?

Actually it can be done this way:

import os

for item, value in os.environ.items():
    print('{}: {}'.format(item, value))

Or simply:

for i, j in os.environ.items():
    print(i, j)

For viewing the value in the parameter:

print(os.environ['HOME'])

Or:

print(os.environ.get('HOME'))

To set the value:

os.environ['HOME'] = '/new/value'

Environment variables are accessed through os.environ:

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

To see a list of all environment variables:

print(os.environ)

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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))

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