tf2_py cannot work with python3

[randoms]

compile tf2_py with python3 , cannot import tf2_py

import tf2_py

ImportError: No module named '_tf2'

[tfoote]

How did you compile and setup your environment? There have been PRs recently merged that have been tested using python3. Such as #173

[randoms]

I used virtualenv

source my_work_space
virtualenv -p /usr/bin/python3 venv
source venv/bin/activate
catkin_make

python packages were installed in my_workspace/devel/lib/python3/dist-packages/
start a ipython console
By defaullt /devel/lib/python3/dist-packages/ is not in sys.path, so I added it to sys.path.

[randoms]

If I cd to tf2_py install path and import _tf2, I got the following error

ImportError: dynamic module does not define init function (PyInit__tf2)

tf2_py/src/tf2_py.cpp#L635
defined PyInit_tf2, should that be PyInit__tf2?

[randoms]

I found a way to make it work with python3
tf2_py/src/tf2_py.cpp#L635
from

PyMODINIT_FUNC PyInit_tf2()

to

PyMODINIT_FUNC PyInit__tf2()

tf2_py/src/tf2_py/init.py#L37
from

from _tf2 import *

to

from ._tf2 import *

[tfoote]

Reading through the documentation it does look like the extra underscore is needed: http://python3porting.com/cextensions.html

@de-vri-es @spaghetti- Did you run into this issue?

[de-vri-es]

Indeed, the extra underscore seems to be required. Note that I'm really only compiling code, not running any runtime tests (they won't run for other reasons, although that got fixed recently I think). Shame it doesn't trigger a linker error though.

I don't think the relative import with a dot works in python2 without from __future__ import absolute_import.

[tfoote]

@randoms could you open a PR with your fixes plus the future import @de-vri-es mentioned?

[randoms]

OK

[jacknlliu]

Is this version released for ROS kinetic with Ubuntu 16.04? I still get the error with latest version.

I clone this repo, and using catkin_make build it, with python2, everything works! but with python3 I still get the following error,

$ python3

>>> from tf import TransformListener
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/tf/__init__.py", line 28, in <module>
    from tf2_ros import TransformException as Exception, ConnectivityException, LookupException, ExtrapolationException
  File "/home/ros/data/tf2_ros/catkin_ws/devel/lib/python2.7/dist-packages/tf2_ros/__init__.py", line 35, in <module>
    exec(__fh.read())
  File "<string>", line 38, in <module>
  File "/home/ros/data/tf2_ros/catkin_ws/devel/lib/python2.7/dist-packages/tf2_py/__init__.py", line 35, in <module>
    exec(__fh.read())
  File "<string>", line 38, in <module>
ImportError: dynamic module does not define module export function (PyInit__tf2)

[jacknlliu]

Could someone reopen this issue? I confirm tf2_py still not work with python3.

[randoms]

From your error message, I think you are loading the python 2.7 version of tf2. To use the python 3 version, you have to compile the source code with python 3. And be careful with your sys.path, python 3 library path should before python 2 library path, make sure to load the right version.