# VTK\_PYTHON\_OPTIONAL\_LINK
**URL:** https://discourse.vtk.org/t/vtk-python-optional-link/484
**Category:** Development
**Created:** [March 14, 2019, 3:41am UTC](https://discourse.vtk.org/t/vtk-python-optional-link/484 "2019-03-14T03:41:30Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@amaclean](https://discourse.vtk.org/u/amaclean)
#### Post date: [March 14, 2019, 3:41am UTC](https://discourse.vtk.org/t/vtk-python-optional-link/484/1 "2019-03-14T03:41:30Z")
In Windows using Anaconda Python 3.7.1, I had to switch this off in order to get a build. I was getting the following error:
`LINK : fatal error LNK1104: cannot open file 'python37.lib'`
It relates to this commit:
Merge topic ‘reenable-vtk-python-optional-link’
4c9c2e1a7a Remove the block preventing the use of VTK\_PYTHON\_OPTIONAL\_LINK
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### Author:  [@ben.boeckel](https://discourse.vtk.org/u/ben.boeckel)
#### Post date: [March 14, 2019, 1:35pm UTC](https://discourse.vtk.org/t/vtk-python-optional-link/484/2 "2019-03-14T13:35:01Z")
Hmm. Our buildbots probably aren’t using 3.13 yet, so were oblivious to it.
Cc: @scottwittenburg The conditional check should probably be `APPLE` rather than `FALSE` while the other platform issues are tracked down.
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### Author:  [@scottwittenburg](https://discourse.vtk.org/u/scottwittenburg)
#### Post date: [March 14, 2019, 2:11pm UTC](https://discourse.vtk.org/t/vtk-python-optional-link/484/3 "2019-03-14T14:11:28Z")
Is that because it seems to be working on OSX? Is that a better way forward for the moment that reverting the previous topic?
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### Author:  [@ben.boeckel](https://discourse.vtk.org/u/ben.boeckel)
#### Post date: [March 19, 2019, 2:39pm UTC](https://discourse.vtk.org/t/vtk-python-optional-link/484/4 "2019-03-19T14:39:40Z")
I think whatever we end up doing, a round of ParaView testing needs to be done before it lands in VTK again.
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### Author:  [@toddy](https://discourse.vtk.org/u/toddy)
#### Post date: [April 7, 2021, 3:30am UTC](https://discourse.vtk.org/t/vtk-python-optional-link/484/5 "2021-04-07T03:30:53Z")
I also had to set
**VTK\_PYTHON\_OPTIONAL\_LINK=OFF**
and
**VTK\_WINDOWS\_PYTHON\_DEBUGGABLE=ON**
to get it to build with Visual Studio 2017 on Windows 10 from the VTK master branch
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### Author:  [@ben.boeckel](https://discourse.vtk.org/u/ben.boeckel)
#### Post date: [April 7, 2021, 12:23pm UTC](https://discourse.vtk.org/t/vtk-python-optional-link/484/6 "2021-04-07T12:23:42Z")
I suspect that the `VTK::Python` code needs an update in the face of `VTK_WINDOWS_PYTHON_DEBUGGABLE` to use the debug library target. I don’t have Windows handy at the moment, but if you want to delve in, changing the `vtk_python_target` variable based on it would be the place to focus on.
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### Author:  [@toddy](https://discourse.vtk.org/u/toddy)
#### Post date: [April 8, 2021, 1:34am UTC](https://discourse.vtk.org/t/vtk-python-optional-link/484/7 "2021-04-08T01:34:14Z")
It turns out **VTK\_PYTHON\_OPTIONAL\_LINK** is off and hidden by default on Windows, so that wasn’t the issue.
The solution seems to be that **VTK\_WINDOWS\_PYTHON\_DEBUGGABLE** should default to **ON** when building in debug mode, but I think that would require a feature change for CMake _**cmake\_dependent\_option()**_
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### Author:  [@ben.boeckel](https://discourse.vtk.org/u/ben.boeckel)
#### Post date: [May 18, 2021, 5:42pm UTC](https://discourse.vtk.org/t/vtk-python-optional-link/484/8 "2021-05-18T17:42:02Z")
Could you please file an issue describing the problem?
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### Author:  [@toddy](https://discourse.vtk.org/u/toddy)
#### Post date: [May 18, 2021, 10:21pm UTC](https://discourse.vtk.org/t/vtk-python-optional-link/484/9 "2021-05-18T22:21:24Z")
See [https://gitlab.kitware.com/vtk/vtk/-/issues/17749](https://gitlab.kitware.com/vtk/vtk/-/issues/17749). The problem seems to be here.
Setting **VTK\_WINDOWS\_PYTHON\_DEBUGGABLE=ON** prevents UNDEF\_DEBUG but this then requires some other trickery to get the python wrappers to use the release version - described here [https://gitlab.kitware.com/paraview/paraview/-/issues/19428#note\_919269](https://gitlab.kitware.com/paraview/paraview/-/issues/19428#note_919269)