+ """Given a keyword, return the set of MAC address(es) that have
+ that keyword.
+
+ >>> reg = SmartHomeRegistry('/home/scott/bin/network_mac_addresses.txt')
+ >>> r = reg.get_macs_by_keyword('test')
+ >>> e = set(['34:29:8F:12:26:74' , '34:29:8F:12:34:8E'])
+ >>> r == e
+ True
+
+ >>> reg.get_macs_by_keyword('unknown')
+ set()
+
+ """