This fix did not work for me - I dont have the type locally, so RosPack cannot find it:

$ rosmsg show -b my.bag packageYYY/messageZZZ
Unable to load msg [packageYYY/messageZZZ]: Cannot locate message [messageZZZ]: unknown package [packageYYY] on search path [....]

What does fix the problem for me is just printing the full text of pytype:

          datatype, _, _, _, pytype = msg
           if datatype == arg:
               print(pytype._full_text)
               break

I only tried the patch with a message which was available on the system.

The snippet you posted does not take the --raw option into account. I updated the patch to support messages not available on the system and handle --raw but the change depends on a change to genpy to expose the specs for the dynamically created message (see ros/genpy#75).

Right, I forgot about the --raw option... I tested the changes locally (both with and without --raw) and it works as expected. 👍

Thanks for trying the patch and reporting back!

This needs to wait until ros/genpy#75 has been released and can be backported to Kinetic.