python3 guard for using rosmsg codec (take 2)

[dirk-thomas]

Replaces #133 (since I didn't have permissions to push to the forked branch) and closes #132.

This patch makes the remaining code for the custom codec error handler conditional on the Python version.

@gwendolynbrook @mikepurvis FYI

[mikepurvis]

If we're here anyway, should we check hasattr(genpy, 'RosMsgUnicodeErrors') before registering the handler, to cover the case where genpy is older on the target system than the machine that built the messages?

[dirk-thomas]

should we check hasattr(genpy, 'RosMsgUnicodeErrors') before registering the handler

I am not sure I understand the proposed change. The registration (https://github.com/ros/genpy/pull/134/files#diff-f4626899ff80377c1eaf9d092e00785eR88) happens directly after defining the RosMsgUnicodeErrors class so I don't see how this needs to be conditional.

to cover the case where genpy is older on the target system than the machine that built the messages?

Wouldn't that require all using code (.decode('utf-8', 'rosmsg')) to only use the custom error handler conditionally?

[mikepurvis]

Oh shoot, sorry yes— yeah, that would be much more invasive of a change. Disregard.

[mikepurvis]

Sorry for all the drama this ended up causing. :(

[dirk-thomas]

@mikepurvis No worry, all changes have a risk (which could have been avoided if this repo would have a noetic-devel branch). So this isn't on you alone 😉

[gwendolynbrook]

@dirk-thomas @mikepurvis thanks for taking care of this (and apologies for the lag on my end; busy week + emails got sorted to spam 🤦 )

[dirk-thomas]

@gwendolynbrook can you please still answer my previous question since that will determine if the merged pull request needs to be released soon or isn't urgent and might not be released at all.

[gwendolynbrook]

@dirk-thomas this questin? #132 (comment) (or am I missing another one?)

[dirk-thomas]

@dirk-thomas this questin? #132 (comment)

Yes.