Unable to use cv_bridge with ROS Kinetic and Python3

I have anaconda3 installed in my system and I face a similar issue while using cv_bridge. When I try to build using catkin build cv_bridge it throws up an error. I use python3.7 from conda. My catkin cofig command is:

catkin config -DPYTHON_EXECUTABLE=/home/akashbaskaran/anaconda3/bin/python3 -DPYTHON_INCLUDE_DIR=/home/akashbaskaran/anaconda3/include/python3.7m -DPYTHON_LIBRARY=/home/akashbaskaran/anaconda3/lib/libpython3.7m.so

Solution: There are a couple of things which I did and the issue got resolved.

• since anaconda is being used, the executables and include directorires should be the one inside your current virtual enviroment. -DPYTHON_EXECUTABLE=/home/akashbaskaran/anaconda3/envs/tf/bin/python3.6 -DPYTHON_INCLUDE_DIR=/home/akashbaskaran/anaconda3/envs/tf/include/python3.6m -DPYTHON_LIBRARY=/home/akashbaskaran/anaconda3/envs/tf/lib/libpython3.6m.so e
• I was having build issues when I tried catkin build cv_bridge. If you face a similar issue, delete all folders except src. Then run catkin_make from the terminal (make sure you are present inside catkin_workspace).
• source the current workspace source devel/setup.bash

Now import cv2 from cv_bridge.boost.cv_bridge_boost import getCvType

should work without an error.

You are right, you should build cv_bridge with python3.

You can do it with passing

-DPYTHON_EXECUTABLE=/usr/bin/python3 -DPYTHON_INCLUDE_DIR=/usr/include/python3.5m -DPYTHON_LIBRARY=/usr/lib/x86_64-linux-gnu/libpython3.5m.so

args to cmake. Or, if you are using catkin to build packages, you can do next steps:

# `python-catkin-tools` is needed for catkin tool
# `python3-dev` and `python3-catkin-pkg-modules` is needed to build cv_bridge
# `python3-numpy` and `python3-yaml` is cv_bridge dependencies
# `ros-kinetic-cv-bridge` is needed to install a lot of cv_bridge deps. Probaply you already have it installed.
sudo apt-get install python-catkin-tools python3-dev python3-catkin-pkg-modules python3-numpy python3-yaml ros-kinetic-cv-bridge
# Create catkin workspace
mkdir catkin_workspace
cd catkin_workspace
catkin init
# Instruct catkin to set cmake variables
catkin config -DPYTHON_EXECUTABLE=/usr/bin/python3 -DPYTHON_INCLUDE_DIR=/usr/include/python3.5m -DPYTHON_LIBRARY=/usr/lib/x86_64-linux-gnu/libpython3.5m.so
# Instruct catkin to install built packages into install place. It is $CATKIN_WORKSPACE/install folder
catkin config --install
# Clone cv_bridge src
git clone https://github.com/ros-perception/vision_opencv.git src/vision_opencv
# Find version of cv_bridge in your repository
apt-cache show ros-kinetic-cv-bridge | grep Version
    Version: 1.12.8-0xenial-20180416-143935-0800
# Checkout right version in git repo. In our case it is 1.12.8
cd src/vision_opencv/
git checkout 1.12.8
cd ../../
# Build
catkin build cv_bridge
# Extend environment with new package
source install/setup.bash --extend

And

$ python3

Python 3.5.2 (default, Nov 23 2017, 16:37:01) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from cv_bridge.boost.cv_bridge_boost import getCvType
>>> 

If you encountered an next error

CMake Error at /usr/share/cmake-3.5/Modules/FindBoost.cmake:1677 (message):
  Unable to find the requested Boost libraries.

  Boost version: 1.58.0

  Boost include path: /usr/include

  Could not find the following Boost libraries:

          boost_python3

  No Boost libraries were found.  You may need to set BOOST_LIBRARYDIR to the
  directory containing Boost libraries or BOOST_ROOT to the location of
  Boost.
Call Stack (most recent call first):
  CMakeLists.txt:11 (find_package)

It is because CMake tries to find libboost_python3.so library, but in ubuntu it is libboost_python-py35.so(/usr/lib/x86_64-linux-gnu/libboost_python-py35.so), so you should change line

find_package(Boost REQUIRED python3)

to

find_package(Boost REQUIRED python-py35)

in file src/vision_opencv/cv_bridge/CMakeLists.txt and rebuild package.