String concatenation using + is generally not recommended, mostly due to performance issues, because strings are immutable. You can use string formatting instead:

    '{}-{}-{}'.format(os_info, pi.package, pi.version)

or if you prefer:

    '{0}-{1.package}-{1.version}'.format(os_info, pi)

Or if you find this more legible:

    '{os_info}-{pi.package}-{pi.version}'.format(os_info=os_info, pi=pi)

There's also another string formatting format using the percent symbol, but the format method is the future (http://stackoverflow.com/q/12382719/284318):

    '%s-%s-%s' % (os_info, pi.package, pi.version)