# PsychoPy 2026.2.3/2026.2.4 cannot launch on macOS 27

**URL:** <https://discourse.psychopy.org/t/psychopy-2026-2-3-2026-2-4-cannot-launch-on-macos-27/47891>\
**Category:** Other\
**Tags:** mac\
**Created:** [September 15, 2026, 7:15am UTC](https://discourse.psychopy.org/t/psychopy-2026-2-3-2026-2-4-cannot-launch-on-macos-27/47891 "2026-09-15T07:15:24Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![psyboo](https://avatars.discourse-cdn.com/v4/letter/p/ad7895/32.png) [@psyboo](https://discourse.psychopy.org/u/psyboo)\
**Post date:** [September 15, 2026, 7:15am UTC](https://discourse.psychopy.org/t/psychopy-2026-2-3-2026-2-4-cannot-launch-on-macos-27/47891/1 "2026-09-15T07:15:24Z")

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Hi everyone,

I am experiencing a launch error with PsychoPy Standalone on a new Apple Silicon Mac, and I would appreciate any help identifying the cause.

System:

- MacBook Air with Apple M5
- macOS 27
- System locale: zh\_CN.UTF-8

PsychoPy versions tested:

- PsychoPy 2026.2.3 macOS arm64, Python 3.10
- PsychoPy 2026.2.3 macOS arm64, Python 3.11
- PsychoPy 2026.2.4 macOS arm64, Python 3.10
- PsychoPy 2026.2.4 macOS arm64, Python 3.11

All four builds fail immediately at launch with the same type of py2app “Launch error”.

I have already tried the following:

1. Removed PsychoPy and reinstalled it.

2. Used AppCleaner to remove PsychoPy and related files, then performed a clean reinstall.

3. Renamed the existing `.psychopy3` folder so PsychoPy would create a completely fresh configuration directory.

4. Renamed/recreated `userPrefs.cfg` and `appData.cfg`.

5. Changed macOS preferred languages to English only.

6. Tried launching PsychoPy directly from Terminal with an English locale:

None of these solved the problem.

My current Terminal locale is:

LANG=“zh\_CN.UTF-8”  
LC\_COLLATE=“zh\_CN.UTF-8”  
LC\_CTYPE=“zh\_CN.UTF-8”  
LC\_MESSAGES=“zh\_CN.UTF-8”  
LC\_MONETARY=“zh\_CN.UTF-8”  
LC\_NUMERIC=“zh\_CN.UTF-8”  
LC\_TIME=“zh\_CN.UTF-8”  
LC\_ALL=

With a fresh `.psychopy3` directory, PsychoPy crashes before `userPrefs.cfg` or `appData.cfg` are even created.

For PsychoPy 2026.2.4 macOS arm64 with Python 3.10, the current `last_app_load.log` is:

Traceback (most recent call last):  
File “/Applications/PsychoPy.app/Contents/Resources/ **boot**.py”, line 262, in  
\_run()  
File “/Applications/PsychoPy.app/Contents/Resources/ **boot**.py”, line 185, in \_run  
exec(compile(source, path, “exec”), globals(), globals())  
File “/Applications/PsychoPy.app/Contents/Resources/psychopyApp.py”, line 207, in  
main()  
File “/Applications/PsychoPy.app/Contents/Resources/psychopyApp.py”, line 196, in main  
\_ = startApp(  
File “/Applications/PsychoPy.app/Contents/Resources/lib/python3.10/psychopy\_app/ **init**.py”, line 130, in startApp  
\_psychopyAppInstance = PsychoPyApp(  
File “/Applications/PsychoPy.app/Contents/Resources/lib/python3.10/psychopy\_app/\_psychopyApp.py”, line 256, in **init**  
if not wx.Locale.IsAvailable(locale):  
wx.\_core.wxAssertionError: C++ assertion “lang == wxLANGUAGE\_DEFAULT” failed at /private/var/folders/yz/zr09txvs5dn18vt4cn21kzl40000gn/T/cibw-sdist-6srn\_ms4/wxpython-4.2.5/ext/wxWidgets/src/common/intl.cpp(781) in IsAvailable(): No info for a valid language?

The Python 3.11 build of PsychoPy 2026.2.4 fails at the same `wx.Locale.IsAvailable(locale)` call.

PsychoPy 2026.2.3 also produced essentially the same error with both Python 3.10 and 3.11.

Since the error persists across:

- two PsychoPy versions,
- both Python 3.10 and 3.11 builds,
- a completely fresh `.psychopy3` directory,
- English-only macOS preferred languages,
- and an explicitly forced `en_US.UTF-8` environment,

I am wondering whether this may be a compatibility issue between PsychoPy Standalone / wxPython / wxWidgets and macOS 27.

Has anyone reproduced this on macOS 27, or is there another workaround I could try?

Thank you very much!

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<div class="post-metadata">

**Author:** ![h.ashida](https://avatars.discourse-cdn.com/v4/letter/h/85e7bf/32.png) [@h.ashida](https://discourse.psychopy.org/u/h.ashida)\
**Post date:** [October 20, 2026, 10:40pm UTC](https://discourse.psychopy.org/t/psychopy-2026-2-3-2026-2-4-cannot-launch-on-macos-27/47891/2 "2026-10-20T22:40:49Z")

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I am having very similar problems after 2026.2.0 on M1/M4 Macs running macOS 26.

PsychoPy starts up on some Macs but not on others.

Even on the same Mac, it works for one user but not for others. It fails on a newly created user account. Locale settings (env values) seem to be the same but I am not sure.

Does anyone have any idea what I should check?

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**Author:** ![TParsons](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/tparsons/32/8301_2.png) [@TParsons](https://discourse.psychopy.org/u/TParsons)\
**Post date:** [October 21, 2026, 11:06am UTC](https://discourse.psychopy.org/t/psychopy-2026-2-3-2026-2-4-cannot-launch-on-macos-27/47891/3 "2026-10-21T11:06:16Z")

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It could be yes; what seems to be happening is it’s asking the operating system what language it’s set to and getting back an answer which wxPython doesn’t recognise as a valid locale code.

You could work around it by editing `userPrefs.cfg` in a text editor to explicitly give a locale code, which will avoid the problem line altogether as if it’s explicitly told what language to translate to it won’t bother asking the operating system. The line to look for in `userPrefs.cfg` is:

```auto
locale = ''

```

If you change it to e.g.

```auto
locale = 'en-US'

```

it should skip the bit that fails.

Annoyingly wxPython don’t list the values of supported locale codes online (as far as I could find at least) but they do list the names they give them [here](https://docs.wxpython.org/wx.Language.enumeration.html#wx-language), so if you use one of the matching locale codes from [here](https://simplelocalize.io/data/locales/) I expect one of them will work (e.g. `wx.LANGUAGE_PUNJABI` will be one of `pa-AW` or `pa-CW`, or possibly just `pa`).

It’s tricky to fix this properly as if we can’t detect the OS language through wxPython then there’s not a lot to work with, but what we can do (and I’ll put this in as a fix for the next release) is catch the error and revert to `en-US` so that at least the app will open and you can explicitly choose a preferred language without having to manually go and edit the userPrefs.cfg text file.

Incompatibilities like this are part of the reason we’ve made [PsychoPy Studio](https://discourse.psychopy.org/t/introducing-psychopy-studio/46646) - using a more modern and better maintained system for the front-end application means issues like this are much less common (not that there’s no bugs; but that bugs are usually our fault and therefore easy for us to fix, rather than being the result of an old and poorly maintained UI package which we don’t have any control over). So if you’re able I’d recommend giving Studio a go!

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<div class="post-metadata">

**Author:** ![h.ashida](https://avatars.discourse-cdn.com/v4/letter/h/85e7bf/32.png) [@h.ashida](https://discourse.psychopy.org/u/h.ashida)\
**Post date:** [October 21, 2026, 12:48pm UTC](https://discourse.psychopy.org/t/psychopy-2026-2-3-2026-2-4-cannot-launch-on-macos-27/47891/4 "2026-10-21T12:48:25Z")

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Dear TParsons,

Thank you very much! It worked!!

So, clearing up userPref.cfg to default does not help. Now my problem is how to instruct students in the class who have never used Terminal or opened folders beginning with a dot. It might be helpful if the default locale in the file is ‘en-US’ (or whatever more appropriate) rather than ‘’.

I would love to try Studio at some point, but now I simply do not have time before my class in a week.

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<div class="post-metadata">

**Author:** ![psyboo](https://avatars.discourse-cdn.com/v4/letter/p/ad7895/32.png) [@psyboo](https://discourse.psychopy.org/u/psyboo)\
**Post date:** [October 22, 2026, 3:06am UTC](https://discourse.psychopy.org/t/psychopy-2026-2-3-2026-2-4-cannot-launch-on-macos-27/47891/5 "2026-10-22T03:06:06Z")

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Thank you so much for your helpful advice and support! I’ve installed the latest PsychoPy Studio, and everything is now running smoothly on my Mac. I really appreciate you taking the time to look into this and help me out. Thanks again!