cmake: VTK_PYTHON_VERSION ignored, python 3.5 not found (VTK 8.2, ubuntu 16.04)

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1

I’m trying to build VTK 8.2 with bindings for python 3.5, so I set VTK_PYTHON_VERSION=3 (or 3.5), but cmake can’t find it, it finds just 2.7 instead:

Could NOT find PythonInterp: Found unsuitable version “2.7.12”, but
required is at least “3” (found /usr/bin/python2)

I googled, found a suggestion to force PYTHON_EXECUTABLE=/usr/bin/python3 (which DOES exist), but then I get an error about libraries mismatch:

CMake Warning at CMake/vtkPythonWrapping.cmake:14 (message):
Python library 2.7 mismatches python 3.5.

I tried to force PYTHON_LIBRARIES, but I still get the mismatch warning. Here’s the line:

cmake -DPYTHON_EXECUTABLE=/usr/bin/python3 -DPYTHON_LIBRARIES=/usr/lib/python3.5/config-3.5m-x86_64-linux-gnu/libpython3.5.so -DVTK_PYTHON_VERSION=3 -S VTK-8.2.0 -B VTK-8.2.0.build/

If I ignore the warnings and go ahead and build, it builds only bindings for 2.7 (in VTK-8.2.0.build/lib/python2.7, nothing for 3.5)

Any idea what’s going on, and how can I fix this? Alternatively, is there a wheel somewhere for VTK 8.2 and python 3.5 for ubuntu 16.04? The pip3 version of VTK is 8.1.x, which I had to hack to make it work with PySide2, but 8.2 should have that fixed that’s why I’m trying to install it.

2

This is an output variable of FindPythonLibs. Set PYTHON_LIBRARY instead.

3

thanks @ben.boeckel, it works!
At first I was still getting the mismatched libraries message, but after clearing the cmake cache it went away.

4

Another note (for some this is obvious, but I’m sure many noobs like me with find this helpful):
I had to also set PYTHONPATH to make ‘import vtk’ work: ‘sudo make install’ puts the package in ‘/usr/local/lib/python3.5/site-packages’, which is not in the search path for imports. Under ubuntu (and other distributions derived from debian), we find instead ‘/usr/local/lib/python3.5/dist-packages’, which is the destination for packages installed by pip(3). I’ve done this by adding this line to /etc/environment:

PYTHONPATH="/usr/local/lib/python3.5/site-packages"

(I didn’t come up with this solution myself, I found it online, but unfortunately I haven’t saved the links)

5

That install path can be changed via the build’s cache entries.

6

That’s even better. Do you remember the name of the variable?

7

Ah, it’s not in the cache by default. VTK_PYTHON_SITE_PACKAGES_SUFFIX

8

I would be cautious with manual installation of VTK python modules to *buntu’s dist-packages though. That is reserved for things installed through Ubuntu packages. I would install VTK as a whole to a non-system-wide prefix and point PYTHONPATH / LD_LIBRARY_PATH there.