Consider using Python 3

[okalachev]

@goldarte, @korigod

[okalachev]

Traceback (most recent call last):
  File "./tests3.py", line 18, in <module>
    import tf2_ros
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/tf2_ros/__init__.py", line 38, in <module>
    from tf2_py import *
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/tf2_py/__init__.py", line 38, in <module>
    from ._tf2 import *
ImportError: dynamic module does not define module export function (PyInit__tf2)

[sfalexrog]

@okalachev, you're seeing these errors because tf2_py was not built against Python 3. As it stands (if I understood ros-infrastructure/rep#149 correctly, even though it is a draft), you need to build all of your packages against Python 3 to have Python 3 support. Even then, you'd have to be at least on Melodic (and see #135 and our internal discussion on that).

We could (and should, really) build the required packages against Python 3 and package them in a separate repository. Whether we should create a public image with Python 3 and ROS Melodic is up for debate, though.

[okalachev]

#215