Python 3.11 + windows-latest → "Tcl wasn't installed properly." randomly happens

[34j]

Description:

The following error sometimes (randomly) occurs (and sometimes does not) when trying to use maplotlib on GitHub Actions with Python 3.11 + windows-latest. Does not happen with Python 3.12, 3.10 and/or Linux, MacOS.

>       self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
E       _tkinter.TclError: Can't find a usable init.tcl in the following directories: 
E           {C:\hostedtoolcache\windows\Python\3.11.9\x64\tcl\tcl8.6}
E       
E       C:/hostedtoolcache/windows/Python/3.11.9/x64/tcl/tcl8.6/init.tcl: couldn't read file "C:/hostedtoolcache/windows/Python/3.11.9/x64/tcl/tcl8.6/init.tcl": No error
E       couldn't read file "C:/hostedtoolcache/windows/Python/3.11.9/x64/tcl/tcl8.6/init.tcl": No error
E           while executing
E       "source C:/hostedtoolcache/windows/Python/3.11.9/x64/tcl/tcl8.6/init.tcl"
E           ("uplevel" body line 1)
E           invoked from within
E       "uplevel #0 [list source $tclfile]"
E       
E       
E       This probably means that Tcl wasn't installed properly.

Action version:
5.6.0

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• Self-hosted

Tools version:

3.11

Repro steps:
Same repo status and

• failure: https://github.com/34j/jordan-form/actions/runs/14952432754/job/42003681865#step:6:146
• success: https://github.com/34j/jordan-form/actions/runs/14952432754/job/42003775605

Expected behavior:
Always succeed

Actual behavior:
Not always succeed, have to re-run until succeed

[aparnajyothi-y]

Hello @34j, Thank you for creating this issue and we will look into it :)

[priya-kinthali]

Hello @34j👋,
Thank you for reporting this issue and providing detailed steps to reproduce it.
We have attempted to replicate the error on our end but have not been able to do so. Based on the error logs and the workflow you shared, it appears that the issue is likely not related to the setup-python action or the hosted runner, but may instead originate from upstream dependencies specifically with CPython's handling of virtual environments or the uv environment manager.
The error message 'tkinter.TclError: Can't find a usable init.tcl' suggests that the Tkinter is unable to locate the necessary Tcl/Tk files, which may be related to how uv configures the virtual environment and manages the paths to these resources.

Here are some related discussions for your reference::

• There is a related issue in CPython (python/cpython#125235), where Tkinter applications fail to start in a virtual  environment. A fix for this issue is included in Python 3.13.1 (python/cpython#125312).
• The uv repository also has similar discussions regarding environment setup that might be relevant.

Given that the issue appears to be upstream, we recommend reviewing the resources above. If the problem persists, please consider raising the issue in the uv or CPython repositories to receive more targeted assistance.

We hope this helps. Please let us know if you have any further concerns. Thank you!