Noetic and Python 3 Plan

[sloretz]

Is there a plan for this repo to support Noetic and Python 3? In case you haven't seen it, there's a tutorial on the ROS wiki about transitioning to Python 3.

It looks like vision_opencv does not have a source entry for Noetic and is directly blocking 54 other repos. A source entry signals to other packages it is being worked on, and makes it possible for downstream maintainers to use rosinstall_generator to download their dependencies while they work on Python 3 incompatibilities.

For starters, these rosdep keys will need to be switched to python 3 equivalents, and all the equivalents already exist:

• python -> python3
• python-opencv -> python3-opencv
• python-numpy -> python3-numpy

vision_opencv/cv_bridge/package.xml

Lines 24 to 25 in 0bbebb7

	<build_depend>python</build_depend>
	<build_depend>python-opencv</build_depend>

vision_opencv/cv_bridge/package.xml

Lines 31 to 32 in 0bbebb7

	<exec_depend>python</exec_depend>
	<exec_depend>python-opencv</exec_depend>

vision_opencv/cv_bridge/package.xml

Line 38 in 0bbebb7

<test_depend>python-numpy</test_depend>

[Rayman]

Something like this?

    <depend condition="$ROS_PYTHON_VERSION == '2'">python-numpy</depend>
    <depend condition="$ROS_PYTHON_VERSION == '3'">python3-numpy</depend>

[sloretz]

Yup, minus the single quotes. The package.xml format will need to be bumped to 3 too.

See rospy's package.xml and ros/genpy#104 for examples of conditional dependencies on ROS_PYTHON_VERSION.

[hhansen-bdai]

Just commenting here to show my interest in also getting this to Noetic/Python3 compatibility

[seanyen]

Commenting here for another Python3 related issue:

vision_opencv/cv_bridge/CMakeLists.txt

Line 11 in 0bbebb7

find_package(Boost REQUIRED python3)

On Windows, the naming scheme to look for boost python 3 is little different from Debian/Ubuntu. In this particular case, I have to change it to look for python37 to match my run-time. The similar issue is also discussed here: https://gitlab.kitware.com/cmake/cmake/issues/16391

We probably need a more robust way to find boost python 3 module.

UPDATED:
Adding related docs: https://cmake.org/cmake/help/latest/module/FindBoost.html

Note that Boost Python components require a Python version suffix (Boost 1.67 and later), e.g. python36 or python27 for the versions built against Python 3.6 and 2.7, respectively. This also applies to additional components using Python including mpi_python and numpy. Earlier Boost releases may use distribution-specific suffixes such as 2, 3 or 2.7. These may also be used as suffixes, but note that they are not portable.

UPDATED:
https://cmake.org/cmake/help/v3.13/module/FindPythonLibs.html

Deprecated since version 3.12: Use FindPython3, FindPython2 or FindPython instead.

[sloretz]

Hey @vrabaud, friendly ping. What's the plan for vision_opencv supporting Python 3 and ROS Noetic?

[mjcarroll]

@ahcorde is going to work this, PR: #323

[sloretz]

Thanks for releasing! ros/rosdistro#24373