Description of problem:
Formerly (python-ethtool-0.6-5.el6.x86_64) we had

  python -c 'import ethtool;print ethtool.get_interfaces_info("an invalid name of a device")[0].get_ipv6_addresses()'
  ()

but recently (python-ethtool-0.10-1.fc20.x86_64) this has changed to

  Traceback (most recent call last):
    File "<string>", line 1, in <module>
  SystemError: error return without exception set

Version-Release number of selected component (if applicable):
python-ethtool-0.10-1.fc20.x86_64

How reproducible:
100%

It may make sense to raise an exception if the ethtool.etherinfo object for the device is invalid, but it should be a more specific SystemError.