Getting MAC addresses from systems
There are a few things that I think could be improved.

Include all required imports

The code uses os.popen() but doesn't import os.  It should.

Consider other platforms

On my Linux machine, there is no getmac command, but one could get the required information via ifconfig.  Consider either passing the command in to the function or making OS-specific versions.

Don't use deprecated functions

The os.popen() command is deprecated since version 2.6.  Use the subprocess module instead.