In the 'ec2_launch_instance.py' file (Example 2.1 on the book) lines 80-81 read:

key_dir = os.expanduser(key_dir)
key_dir = os.expandvars(key_dir)

However, the expanduser and expandvars method appear under the os.path module. The code didn't work on my machine (Python 2.7.8, OSX) till I changed the above lines to:

key_dir = os.path.expanduser(key_dir)
key_dir = os.path.expandvars(key_dir)

am I missing something?