ImportError: dynamic module does not define init function

[RaulFdzbis]

Getting the following error while trying to import kinematics-dynamics:

~$ python
Python 2.7.17 (default, Apr 15 2020, 17:20:14) 
[GCC 7.5.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import kinematics_dynamics
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/kinematics_dynamics.py", line 17, in <module>
    _kinematics_dynamics = swig_import_helper()
  File "/usr/local/lib/python2.7/dist-packages/kinematics_dynamics.py", line 16, in swig_import_helper
    return importlib.import_module('_kinematics_dynamics')
  File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
ImportError: dynamic module does not define init function (init_kinematics_dynamics)

After i quick internet search i have tried with python3, but it looks like it is only installed in the 2.7 version. Any ideas why this may be happening?

[PeterBowman]

I can't reproduce this, same Python version. A quite similar error was reported at https://github.com/roboticslab-uc3m/kinematics-dynamics/issues/147#issuecomment-368910149, but that one was clearly showing a Python 2.7 vs 3.4 mismatch.

Can you paste here the output of grep ^PYTHON ~/repos/kinematics-dynamics/bindings/build/CMakeCache.txt | grep -v INTERNAL?

Also, what is your SWIG version (swig -version)?

[RaulFdzbis]

Here you go!

~$ grep ^PYTHON ~/repos/kinematics-dynamics/bindings/build/CMakeCache.txt | grep -v INTERNAL
PYTHON_EXECUTABLE:FILEPATH=/usr/bin/python3.6
PYTHON_INCLUDE_DIR:PATH=/usr/include/python3.6m
PYTHON_LIBRARY:FILEPATH=/usr/lib/x86_64-linux-gnu/libpython3.6m.so
PYTHON_LIBRARY_DEBUG:FILEPATH=PYTHON_LIBRARY_DEBUG-NOTFOUND
~$ swig -version

SWIG Version 1.3.29

Compiled with g++ [x86_64-unknown-linux-gnu]
Please see http://www.swig.org for reporting bugs and further information

Maybe should I reinstall changing python filepath to 2.7?

[PeterBowman]

Thanks!

SWIG Version 1.3.29

That's a really ancient version of SWIG, probably not compatible with YARP anymore. I'm pretty sure you have SWIG 3.x installed, so please try again with swig3.0 -version. If not, do sudo apt install swig3.0 and proceed again. Also, take a look at the advanced configuration of kin-dyn bindings via ccmake (press t) and check your SWIG_xxx variables. Mine look like these (Ubuntu 18.04):

SWIG_DIR=/usr/share/swig3.0
SWIG_EXECUTABLE=/usr/bin/swig3.0
SWIG_VERSION=3.0.8

Now, make sure you are actually compiling against the Python version you want. Your CMake is configured to pick Python 3.6 development headers. Please check the advanced CMAKE_INSTALL_PYTHONDIR variable. Does it point at /usr/local/lib/python2.7/dist-packages or /usr/local/lib/python3.6/dist-packages? Adjust this variable (if present) and the others you pasted before so that everything refers to the same Python release. There are some pointers in the install guide that offer a workaround for Python 3.x, you might need those as well.

[RaulFdzbis]

This is my ccmake output of bindings:

 PYTHON_EXECUTABLE                /usr/bin/python3.6            
 PYTHON_INCLUDE_DIR               /usr/include/python3.6m     
 PYTHON_LIBRARY                   /usr/lib/x86_64-linux-gnu/libpython3.6m.so
 PYTHON_LIBRARY_DEBUG             PYTHON_LIBRARY_DEBUG-NOTFOUND
....
 SWIG_DIR                         /usr/share/swig3.0
 SWIG_EXECUTABLE                  /usr/bin/swig3.0
 SWIG_VERSION                     3.0.12

I didnt find the CMAKE_INSTALL_PYTHONDIR variable. In my case Kinematics-dynamics was installed on /usr/local/lib/python3/dist-packages/, what I did was:

sudo ln -s /usr/local/lib/python3/dist-packages/_kinematics_dynamics.so /usr/local/lib/python2.7/dist-packages/
sudo ln -s /usr/local/lib/python3/dist-packages/kinematics_dynamics.py /usr/local/lib/python2.7/dist-packages/

[PeterBowman]

I don't think you should mix Python 2.x and 3.x dist-packages as it would probably cause compat issues, I'd remove those symlinks you added. So, what is the actual problem here? You built kin-dyn bindings for Python 3, which got properly installed, now you should be able to load the corresponding module via python3. It obviously won't work that way if you launch the Python 2 interpreter instead. Did you want to compile Python 2 bindings? In that case, please tweak CMake variables to point at Python 2.7 directories and executables and you should be fine.

[RaulFdzbis]

I tried to do an import using python3.6 and it works:

~…/bindings/build (develop)$ python3.6
Python 3.6.9 (default, Apr 18 2020, 01:56:04) 
[GCC 8.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import kinematics_dynamics
>>> 

So maybe reinstall changing paths to 2.7?

[PeterBowman]

So maybe reinstall changing paths to 2.7?

👍

[RaulFdzbis]

Thought the sym links would work haha. I will try it and close the issue if everything goes right.

Thank you very much Bartek!

[RaulFdzbis]

Deleted symlinks, changed ccmake bindings to

 PYTHON_EXECUTABLE                /usr/bin/python2.7            
 PYTHON_INCLUDE_DIR               /usr/include/python2.7      
 PYTHON_LIBRARY                   /usr/lib/x86_64-linux-gnu/libpython2.7.so

and is working. Thank you again @PeterBowman