Run rospy inside Jython

edit

I'm not sure what you're getting at. Should I add to Jython /opt/ros/$ROSDISTRO? By the way I build it from source because Ubuntu 18.04 does not support ROS Kinetic so isntead of /opt/ros/$ROSDISTRO I should have to use ~/ros_catkin_ws.

This would be the right solution. But which is the correct one I have to use?

>>> sys.path.append('/home/openhabvm/ros_catkin_ws/build_isolated')
>>> sys.path.append('/home/openhabvm/ros_catkin_ws/devel_isolated')
>>> sys.path.append('/home/openhabvm/ros_catkin_ws/install_isolated')
>>> import rospy
>>>

Build, Devel or Install?

I am amazed. It didn't work if I left out individual things, and somehow I also have to consider an appropriate order. One also needs:

>>> sys.path.append('/home/openhabvm/ros_catkin_ws')
>>> sys.path.append('/home/openhabvm/ros_catkin_ws/src')

and:

>>> sys.path.append('/usr/local/lib/python2.7/dist-packages')

Well it is not the whole ROS integration. I can not import std_msgs as example. I got this error:

>>> from std_msgs.msg import String
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name String

Of course, I also have a suspicion where this comes from. But I won't be the only one who first comes up with one solution and then looks for the next. It may be possible to link it later, should my project succeed.

I hope no one minds if I expand on this a bit. I could still use some help. Of course it is a different if I run jython or jython -Dpython.path=$PYTHONPATH.

echo $PYTHONPATH
/home/<user>/naoqi/pynaoqi-python2.7-2.5.7.1-linux64:/home/<user>/catkin_ws/devel/lib/python2.7/dist-packages:/home/<user>/ros_catkin_ws/install_isolated/lib/python2.7/dist-packages

$ROS_PACKAGE_PATH
/home/<user>/catkin_ws/src:/home/<user>/ros_catkin_ws/install_isolated/share

Another difference is if I use sys.path.insert or sys.path.append. With insert it seems to be possible to import modules and with append packages. I need to import ROS completely not only a part of it. Because I want to achieve to use ROS in Jython and this means it needs the same behaviour than in Python.

Inside ~/ros_catkin_ws/install_isolated/include are header files for C++. In ~/ros_catkin_ws/devel_isolated we will find maybe the right modules but I do not know how to import it correctly.

ls ~/ros_catkin_ws/devel_isolated/std_msgs/lib/python2.7/dist-packages/std_msgs
__init__.py  __init__.pyc  msg

and

ls ~/ros_catkin_ws/devel_isolated/std_msgs/lib/python2.7/dist-packages/std_msgs/msg
_Bool.py             _Duration.pyc           _Header.py            _Int32.pyc                _MultiArrayLayout.py   _UInt32MultiArray.pyc
_Bool.pyc            _Empty.py               _Header.pyc           _Int64MultiArray.py       _MultiArrayLayout.pyc  _UInt32.py

...

What remains is that you would have to import all paths individually. So if not std_msgs maybe you have to import common_msgs etc. also with sys.path.append. Trying to achieve to use once the append function should lead to the fact that you only ever get from ... import, no matter which Module/Package

I'm not sure whether this is Jython specific behaviour.

For a regular Python interpreter (ie: the one distributed via apt on Ubuntu 18.04), it would suffice to add the base dist-packages to the PYTHONPATH.

sys.path is a Python list. The append(..) and insert(..) methods basically modify that list. The former will add to the end of the list, while the latter allows to you insert new entries in arbitrary locations in that list.

I don't understand how that's related to adding packages or modules. It should not make any difference.

I'm also not sure what the relevance is of ROS_PACKAGE_PATH. It's not used by Python interpreters.

And again: if you have an install space, use that. It's not guaranteed that your devel space will be setup correctly in that case.

@gvdhoorn Thank you for your explanation and help. I think in principle I was on the wrong track anyway. When you import rospy, it wants to work with python either way. So you would actually have to develop some kind of rosjy to solve that. I can't just run that under jython instead of python, I guess. I'm at least right about the imported directory.

python
Python 2.7.17 (default, Feb 27 2021, 15:10:58)
[GCC 7.5.0] on linux2
Type "help", "copyright", "credits" or "license" for more informati                                                                                                on.
>>> import rospy
>>> import imp
>>> imp.find_module('rospy')
(None, '/home/<user>/ros_catkin_ws/install_isolated/lib/python2.                                                                                                7/dist-packages/rospy', ('', '', 5))

I try to explain what I mean:

jython talker.py
Traceback (most recent call last):
  File "talker.py", line 39, in <module>
    import rospy
ImportError: No module named rospy

Here I can not find the rospy. Of course if I use python instead of jython it works. So adding the $PYTHONPATH would help a little bit:

jython -Dpython.path=$PYTHONPATH talker.py
Traceback (most recent call last):
  File "talker.py", line 39, in <module>
    import rospy
  File "/home/openhabvm/ros_catkin_ws/install_isolated/lib/python2.7/dist-packages/rospy/__init__.py", line 47, in <module>
    from std_msgs.msg import Header
  File "/home/openhabvm/ros_catkin_ws/install_isolated/lib/python2.7/dist-packages/std_msgs/msg/__init__.py", line 1, in <module>
    from ._Bool import *
  File "/home/openhabvm/ros_catkin_ws/install_isolated/lib/python2.7/dist-packages/std_msgs/msg/_Bool.py", line 6, in <module>
...

Now it is possible ti import rospy.