from mayavi import mlab ends in error

[dsche-cyber]

After calling python and importing mlab from mayavi, results in error, making mayavi unusable.

python
Python 3.8.6 (default, Sep 30 2020, 04:00:38) 
[GCC 10.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from mayavi import mlab

Error stack:

QStandardPaths: runtime directory '/run/user/1000' is not owned by UID 0, but a directory permissions 0700 owned by UID 1000 GID 1000
QSettings::value: Empty key passed
QStandardPaths: runtime directory '/run/user/1000' is not owned by UID 0, but a directory permissions 0700 owned by UID 1000 GID 1000
QStandardPaths: runtime directory '/run/user/1000' is not owned by UID 0, but a directory permissions 0700 owned by UID 1000 GID 1000
QSettings::value: Empty key passed
/usr/lib/python3.8/site-packages/traits/etsconfig/etsconfig.py:423: UserWarning: Environment variable "HOME" not set, setting home directory to /tmp
  warn(
Traceback (most recent call last):
  File "/usr/lib/python3.8/site-packages/tvtk/tvtk_base.py", line 22, in <module>
    from traits.api import PrefixMap, PrefixList
ImportError: cannot import name 'PrefixMap' from 'traits.api' (/usr/lib/python3.8/site-packages/traits/api.py)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.8/site-packages/mayavi/mlab.py", line 16, in <module>
    from mayavi.tools.camera import view, roll, yaw, pitch, move
  File "/usr/lib/python3.8/site-packages/mayavi/tools/camera.py", line 24, in <module>
    from .engine_manager import get_engine
  File "/usr/lib/python3.8/site-packages/mayavi/tools/engine_manager.py", line 13, in <module>
    from mayavi.core.registry import registry
  File "/usr/lib/python3.8/site-packages/mayavi/core/registry.py", line 16, in <module>
    from mayavi.core.metadata import Metadata, import_symbol
  File "/usr/lib/python3.8/site-packages/mayavi/core/metadata.py", line 11, in <module>
    from mayavi.core.pipeline_info import PipelineInfo
  File "/usr/lib/python3.8/site-packages/mayavi/core/pipeline_info.py", line 12, in <module>
    from .utils import get_tvtk_dataset_name
  File "/usr/lib/python3.8/site-packages/mayavi/core/utils.py", line 6, in <module>
    from tvtk.api import tvtk
  File "/usr/lib/python3.8/site-packages/tvtk/api.py", line 10, in <module>
    from tvtk.tvtk_access import tvtk
  File "/usr/lib/python3.8/site-packages/tvtk/tvtk_access.py", line 55, in <module>
    from tvtk.tvtk_classes import tvtk_helper
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 655, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 618, in _load_backward_compatible
  File "<frozen zipimport>", line 259, in load_module
  File "tvtk_classes/tvtk_helper.py", line 2, in <module>
  File "/usr/lib/python3.8/site-packages/tvtk/tvtk_base.py", line 26, in <module>
    class PrefixMap(Trait):
TypeError: function() argument 'code' must be code, not str

[dsche-cyber]

I solved the Issue for me, but still I think the code needs to be updated, as the exception handling still fails for old traits version.

To fix my Issue I followed the suggestion in Issue #940:
#940 (comment)

So I have now vtk9.0.1-3 from the AUR and installed mayavi-4.7.3dev0 from source.

Further the problem lies in the arch repo packages of traits and traitsui as these are too old (vtk9 seems to be needed by python3.8> and so mayavi-4.7.2> is needed, so the traits packages in the repos do not fit to these newer packages).
To update those I needed to remove other packages too, as it was breaking dependencies:
sudo pacman -R python-traits python-apptools python-envisage python-pyface
Now to update traits:
sudo pip install -U traits traitsui
Then install the packages that were removed before:
sudo pacman -S python-apptools python-envisage python-pyface
Note: I do not know, if those package are required for building other packages under arch, if so it is probably a good idea not to mix pacman and pip installed packages, so alternatively use:
sudo pip install -U apptools envisage pyface
Now it works.