Tested on two different macs (imac and macbook pro) with Sequoia 15.5. After entering the security exception, Slicer icon continues to bounce for about a minute and then quits. When launched from the terminal window from Slicer.app/Contents/MacOS/Slicer, this is the error message:
murat@murats-Mac-mini ~ % pwd
/Users/murat
murat@murats-Mac-mini ~ % /Users/murat/Desktop/Slicer.app/Contents/MacOS/Slicer
Could not find platform independent libraries
Could not find platform dependent libraries <exec_prefix>
Python path configuration:
PYTHONHOME = (not set)
PYTHONPATH = (not set)
program name = ‘Slicer’
isolated = 0
environment = 1
user site = 0
safe_path = 0
import site = 1
is in build tree = 0
stdlib dir = ‘/Users/svc-dashboard/D/P/A/python-install/lib/python3.12’
sys._base_executable = ‘/Users/murat/Desktop/Slicer.app/Contents/MacOS/Slicer’
sys.base_prefix = ‘/Users/svc-dashboard/D/P/A/python-install’
sys.base_exec_prefix = ‘/Users/svc-dashboard/D/P/A/python-install’
sys.platlibdir = ‘lib’
sys.executable = ‘/Users/murat/Desktop/Slicer.app/Contents/MacOS/Slicer’
sys.prefix = ‘/Users/svc-dashboard/D/P/A/python-install’
sys.exec_prefix = ‘/Users/svc-dashboard/D/P/A/python-install’
sys.path = [
‘/Users/svc-dashboard/D/P/A/python-install/lib/python312.zip’,
‘/Users/svc-dashboard/D/P/A/python-install’,
‘/Users/svc-dashboard/D/P/A/python-install/lib-dynload’,
‘/Users/svc-dashboard/D/P/A/python-install/plat-darwin’,
‘/Users/svc-dashboard/D/P/A/python-install/lib/python3.12’,
‘/Users/svc-dashboard/D/P/A/python-install/lib/python3.12/lib-dynload’,
‘/Users/svc-dashboard/D/P/A/python-install/lib-tk’,
‘/Users/svc-dashboard/D/P/A/python-install/lib/python3.12’,
‘/Users/svc-dashboard/D/P/A/python-install/lib/python3.12/lib-dynload’,
]
Fatal Python error: init_fs_encoding: failed to get the Python codec of the filesystem encoding
Python runtime state: core initialized
ModuleNotFoundError: No module named ‘encodings’
Current thread 0x0000000200aaf200 (most recent call first):
I can replicate the same failure to launch (same error message) with Slicer Preview 2025-08-01 on a macbook air m3. 5.8.1 starts fine, as does the SlicerDesigner app from the Preview.
I think those are separate and i believe that error arose because i didnt launch the correct SlicerDesigner, but the Designer application, which didnt set the correct python environment as you mentioned in that thread.
This is the proper Slicer launcher that generates the error.
Does a Slicer preview build from May have the same problem specifically on macOS 15.5? Just wondering if related to changes in macOS security impacting the unsigned Slicer preview builds (Slicer 5.8.1 is a signed version) is a cause here or something in recent Slicer commits.
Failure to launch is a serious issue, so submitting an issue on github makes sense; and then this discussion should continue there. Peobably @jcfr knows most about potential root causes and fixes, but maybe you can help the investigation if you determine which is the first date where the Slicer Preview Release started to fail (you can use the offset option on thr download page to get previous releases, for example Download 3D Slicer | 3D Slicer).
Not sure why it is showing random stable versions, which are clearly dated wrong. Also when I click the 5.9.0 from July 30, the downloaded package shows as Slicer-5.9.0-2025-07-25-macosx-amd64.dmg
because it doesn’t launch, I can’t confirm whether it is indeed the revision 33809 or a different revision number.
