from mayavi import mlab ends in error

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