Assertion and nextEventMatchingMask Error on MacOS when using wx.FileDialog called through flask/dash

[matt-sd-watson]

I am attempting to run a wx.Dialog popup through my flask/dash application with the following calback logic:

import wx
app = wx.App(None)
dialog = wx.FileDialog(None, 'Open', str(Path.home()), style=wx.FD_OPEN | wx.FD_MULTIPLE | wx.FD_FILE_MUST_EXIST,
                                   wildcard="*.tiff;*.tif;*.mcd;*.txt;*.h5;*.h5ad|*.tiff;*.tif;*.mcd;*.txt;*.h5;*.h5ad")
if dialog.ShowModal() == wx.ID_OK:
                filenames = dialog.GetPaths()
                if filenames is not None and len(filenames) > 0 and isinstance(filenames, list):
                    session_config = validate_session_upload_config(cur_session)
                    for filename in filenames: session_config["uploads"].append(filename)
                    dialog.Destroy()
                    return session_config
                dialog.Destroy()
                raise PreventUpdate
      dialog.Destroy()
      raise PreventUpdate
raise PreventUpdate

The dialog opens dynamically when the user selects a button.
This works perfectly fine on both Linux and Windows, but on MacOS I get the following error in the console trace:

2025-01-28 09:03:01.035 Python[16777:412914] WARNING: nextEventMatchingMask should only be called from the Main Thread! This will throw an exception in the future.
2025-01-28 09:03:01.035 Python[16777:412914] *** Assertion failure in +[NSUndoManager _endTopLevelGroupings], NSUndoManager.m:1117
2025-01-28 09:03:01.068 Python[16777:412914] *** Assertion failure in +[NSUndoManager _endTopLevelGroupings], NSUndoManager.m:1117
2025-01-28 09:03:01.077 Python[16777:412914] *** Assertion failure in +[NSUndoManager _endTopLevelGroupings], NSUndoManager.m:1117
2025-01-28 09:03:01.085 Python[16777:412914] *** Assertion failure in +[NSUndoManager _endTopLevelGroupings], NSUndoManager.m:1117
2025-01-28 09:03:01.092 Python[16777:412914] *** Assertion failure in +[NSUndoManager _endTopLevelGroupings], NSUndoManager.m:1117
2025-01-28 09:03:01.097 Python[16777:412914] *** Assertion failure in +[NSUndoManager _endTopLevelGroupings], NSUndoManager.m:1117

My current python environment (3.9.11) is set up with the following:

anndata==0.9.1
async-generator==1.10
attrs==23.1.0
beautifulsoup4==4.12.2
biopython==1.85
cachelib==0.9.0
certifi==2024.7.4
cffi==1.15.1
charset-normalizer==3.1.0
click==8.1.3
click-log==0.4.0
colorspacious==1.1.2
colour==0.1.5
contourpy==1.0.7
coverage==7.6.10
cryptography==43.0.1
cycler==0.11.0
Cython==0.29.35
dash==2.18.2
dash-ag-grid==2.3.0
dash-auth==2.0.0
dash-bootstrap-components==1.4.1
dash-core-components==2.0.0
dash-draggable==0.1.2
dash-extensions==1.0.1
dash-google-auth==0.1.2
dash-html-components==2.0.0
dash-mantine-components==0.12.1
dash-table==5.0.0
dash-testing-stub==0.0.2
dash_bio==1.0.2
dash_canvas==0.1.0
dash_daq==0.5.0
dash_tour_component==0.0.2
dash_uploader==0.7.0a1
dill==0.3.6
diskcache==5.6.1
dnspython==2.7.0
EditorConfig==0.12.3
exceptiongroup==1.1.1
fcswrite==0.6.2
Flask==2.2.5
Flask-Caching==2.0.2
Flask-Dance==7.0.0
Flask-HTTPAuth==4.8.0
fonttools==4.43.0
freeport==0.1.15
GEOparse==2.0.4
glasbey==0.2.0
h11==0.14.0
h5py==3.8.0
idna==3.7
igraph==0.10.4
imagecodecs==2023.9.18
imageio==2.31.0
imctools==2.1.8
importlib-metadata==6.6.0
importlib-resources==5.12.0
iniconfig==2.0.0
itsdangerous==2.1.2
Jinja2==3.1.5
joblib==1.2.0
jsbeautifier==1.14.8
jsonschema==4.23.0
jsonschema-specifications==2024.10.1
kaleido==0.2.1
kiwisolver==1.4.4
lazy_loader==0.2
leidenalg==0.9.1
llvmlite==0.42.0
lxml==4.9.2
MarkupSafe==2.1.3
matplotlib==3.7.1
mongomock==4.1.2
more-itertools==9.1.0
multiprocess==0.70.14
natsort==8.4.0
nest-asyncio==1.6.0
networkx==3.1
numba==0.59.0
numexpr==2.8.8
numpy==1.24.3
oauthlib==3.2.2
opencv-python-headless==4.8.1.78
outcome==1.2.0
packaging==21.3
pandas==2.0.2
ParmEd==4.3.0
patsy==0.5.3
percy==2.0.2
periodictable==2.0.2
PhenoGraph==1.5.7
pillow==10.3.0
plotly==5.14.1
pluggy==1.0.0
psutil==5.9.5
pycparser==2.21
pydantic==1.10.13
pymongo==4.6.3
pynndescent==0.5.10
pyOpenSSL==24.2.1
pyparsing==3.0.9
PySocks==1.7.1
pytest==7.3.1
pytest-cov==4.0.0
python-dateutil==2.8.2
pytz==2023.3
PyWavelets==1.4.1
rakaia @ file:///Users/mattw/github/rakaia
readimc==0.7.0
referencing==0.36.2
requests==2.32.3
requests-oauthlib==1.3.1
retrying==1.3.4
rpds-py==0.22.3
scanpy==1.9.3
scikit-image==0.21.0
scikit-learn==1.5.0
scipy==1.10.1
seaborn==0.12.2
selenium==4.2.0
sentinels==1.0.0
session_info==1.0.0
shortuuid==1.0.12
six==1.16.0
sniffio==1.3.0
sortedcontainers==2.4.0
soupsieve==2.4.1
statsmodels==0.14.0
stdlib-list==0.8.0
steinbock==0.16.1
tenacity==8.2.2
texttable==1.6.7
threadpoolctl==3.1.0
tifffile==2023.8.12
tomli==2.0.1
tqdm==4.66.3
trio==0.22.0
trio-websocket==0.10.2
typing_extensions==4.8.0
tzdata==2023.3
umap-learn==0.5.2
urllib3==1.26.19
urllib3-secure-extra==0.1.0
URLObject==2.4.3
waitress==3.0.1
Werkzeug==3.0.6
wsproto==1.2.0
wxPython==4.2.0
xmltodict==0.13.0
xtiff==0.7.9
zipp==3.19.1

[swt2c]

Hard to say without a small, self-contained example but the error message suggests you might be making wxPython calls from a non-main thread. Is that a possibility?

[matt-sd-watson]

The application is almost certainly running in a multi threaded mode.

[swt2c]

That's likely the problem then. wxPython (GUI) calls have to be made from the main thread.

[matt-sd-watson]

Any insight into the difference in GUI handling for wxPython across different operating systems? When I run my application multi-threaded on either Windows or Linux, the dialog opens and functions perfectly fine.

[swt2c]

You're just getting lucky on Windows and Linux.

You could try wrapping your GUI code with wx.CallAfter():
https://wiki.wxpython.org/CallAfter