How do I access environment variables in Python?

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 the key doesn't exist
print(os.environ.get('KEY_THAT_MIGHT_EXIST'))

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

# Returns `default_value` if the 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

Here's how to check if $FOO is set:

try:  
   os.environ["FOO"]
except KeyError: 
   print "Please set the environment variable FOO"
   sys.exit(1)

You can access the environment variables using

import os
print os.environ

Try to see the content of the PYTHONPATH or PYTHONHOME environment variables. Maybe this will be helpful for your second question.